The Oklahoma Conspiracy: Next Week One Man Will be Executed for Carrying Out America's Worst Peacetime Atrocity

Timothy McVeigh Claims to have Acted Alone. But new Evidence Reveals he was part of an Underground Network of White Supremacists.

Independent - London/May 11, 2001

Imagine this scene in Oklahoma City, in the early morning of 19 April 1995. Timothy McVeigh is driving into town in a rented removal lorry that contains a deadly fertiliser bomb: more than 6,000lbs of ammonium nitrate soaked in nitromethane fuel, supplemented by several sausage-shaped strings of commercial Tovex explosive, all of it wired up to blasting caps and shock tube.

McVeigh has driven down from Kansas, where he spent the previous day making the bomb with his old army buddy and fellow right-wing survivalist Terry Nichols. And now, the deadly plan he has worked on for so long, his gigantic, foolhardy act of revenge against his own government, is about to come to fruition.

The front of his T-shirt bears the slogan shouted by John Wilkes Booth as he assassinated Abraham Lincoln, "Sic semper tyrannis." The back carries a quote from Thomas Jefferson: "The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants."

Shortly before 9am, as he approaches the Alfred P Murrah federal building in improbably sunny weather, McVeigh pops in a pair of earplugs. He lights one five-minute fuse and another two-minute one. He parks in a handicapped- parking zone, right beneath the America's Kids infant daycare centre on the first floor, hops out of the truck and walks away into a series of alleys and streets, taking him safely out of his target's immediate shadow.

His getaway car, a busted-up 18-year-old Mercury Marquis, is parked several blocks away, exactly where he left it four days earlier (again, with Nichols's help). But he has covered barely 150 yards when the deafening roar of the explosion lifts him off his feet, knocks out the glass of the windows all around him, sets off hundreds of car alarms and causes the buildings, even at this distance, to shake violently, sending cascades of brick and stonework into the streets. One-third of the Murrah building has been obliterated, and 168 people - including 19 children - have been killed, in the deadliest peacetime assault on American soil.

That, at least, is Tim McVeigh's version of events. It is the story he gave to two journalists from his hometown of Buffalo, New York, in an extensive series of interviews that forms the centrepiece of the recent book American Terrorist: Timothy McVeigh & the Oklahoma City Bombing. It is clearly the way he would like his act to be remembered, as he prepares for death by lethal injection at a federal penitentiary in Indiana next Wednesday.

It is an account that, for all the media hullaballoo surrounding his execution, has gone largely unquestioned by the US's raucous punditocracy. It is also, give or take a few details, the official version presented by the Federal Bureau of Investigation and government lawyers at his trial in 1997.

McVeigh, the argument ran, had some help from Nichols and another friend from army days, Michael Fortier, but essentially he carried out the bombing alone. No accomplices, no broader network of conspirators, nothing. Case closed, as far as the government was concerned. Now imagine the scene all over again, this time with extra details supplied by eyewitnesses interviewed in the immediate aftermath of the bombing and by the investigative work of a handful of journalists, lawyers and academics who have spent the past six years going over every detail of the calamity to try to wheedle out its mysteries.

Suddenly, the picture is very different. McVeigh is still driving the yellow Ryder removal truck, but he is not alone. The truck contains the unmixed bomb components, minus the detonators and caps which are being transported separately, either in a brown 1970s-era Chevy pick-up or possibly another vehicle.

In the early morning, the vehicles pull up in a derelict section of Bricktown, a mile from the Murrah building, where the accomplices make the bomb at high speed, IRA-style. After filling nine of the 13 barrels in the back of the truck, they run out of nitromethane and switch to diesel fuel.

McVeigh cuts open the Tovex sausages to insert the blasting caps (explaining why traces of PETN, or pentaerythritol tetranitrate, are later found on his clothing).

Then, according to the accounts of at least 10 eyewitnesses, there is a flurry of activity across Oklahoma City in the hour before the bombing. Just after eight o'clock, the brown pick-up roars out of the Murrah building car park with McVeigh and another man inside. Half an hour later, the Ryder truck drives from Bricktown to the top of a hill a mile or so to the north.

It is followed along part of the route by both the pick-up and the Mercury Marquis, the latter with three men inside. The truck waits at a tyre store, possibly for a radio signal giving the all-clear (hence the choice of a high altitude). McVeigh, identified once again as the Ryder driver, allays immediate suspicion by asking the store owner for directions to the Murrah building.

At about 8.45am, the Ryder pulls up across from the Regency Apartments, within sight of the target. Again, at least one person is seen with McVeigh, who goes into a convenience store on the ground floor of the building to buy two Cokes and a pack of cigarettes, even though he does not smoke. At 8.57am, McVeigh pulls into the handicapped zone of the federal building, walks across the street and gets into the Mercury with another man.

From the passenger side of the Ryder truck emerges yet another man, who jumps into the brown pick-up parked just in front and drives away. By the time the bomb explodes at 9.02am, both the Mercury and the pick-up are on the freeway heading north back up to Kansas.

Fact or fantasy? The result of confusion among traumatised eyewitnesses, or an elaborate scheme in which decoys and rapid place- shifting among vehicles are all part of the plan? And who are these supposed accomplices exactly? How many of them are there?

These are the questions that have been gnawing away at investigators and victims of the bombing from day one. The government itself spent more than a year hunting for a so-called "John Doe 2", a second bombing suspect, before giving up and switching its story to the lone-bomber theory.

The original grand jury indictment named McVeigh, Nichols "and others unknown" in what it called a "conspiracy to use a weapon of mass destruction." When the defence team put McVeigh through a polygraph test, he passed on all questions concerning his own role; when asked whether anybody else was involved, however, he failed. The FBI now says the supposition of a wider plot was simply wrong.

Before one dismisses the alternate theory as the stuff of conspiratorial fantasy, however, it is worth examining the deep flaws in the government's side of the story and asking why its early lines of investigation into John Doe 2, the brown pick-up and the rest all came to naught. The reasons are neither as mysterious nor as murkily conspiratorial as one might think.

The government's problem is neatly summarised by Stephen Jones, who, as McVeigh's trial lawyer, had the advantage of examining every document and witness statement gathered by the prosecution. "They got very lucky very early, then their luck turned sour," he said. McVeigh was found in just 48 hours, largely thanks to the fact he had been pulled over on the freeway for a missing back licence plate and remanded in police custody for possession of an illegal concealed weapon.

Nichols gave himself up in Kansas, and Fortier was a logical port of call because McVeigh had stayed extensively at his house in Arizona. But the wider conspiracy proved maddeningly difficult to crack. The people who will be named in this article are well known to the authorities; indeed, most are by now either behind bars for other crimes or dead. At the time of the McVeigh and Nichols trials, however, their relationship to the bombing was either unknown or unsupported by sufficient evidence.

Even the case against McVeigh was riddled with holes, leading several commentators at the time to speculate that he might be acquitted. The government team had to ask itself: should we dilute our case against McVeigh by admitting we can't nail his co-conspirators? Or should we simply pretend they don't exist?

They plumped for the latter, and the fact that McVeigh was convicted and sentenced to death suggests it was indeed a smart strategy to bring to court. That, however, does not make it anything close to the full truth. The government did not call a single eyewitness who saw McVeigh, either in Oklahoma City or in Junction City, Kansas, where the Ryder truck had been rented two days earlier. Why not? Because every one of them saw McVeigh with someone else. At Elliott's Body Shop, the rental agency, there are strong doubts whether McVeigh was seen at all. Although it was his alias, Robert Kling, that was used to secure the rental agreement, neither of the two men described by employees entirely fit McVeigh's profile.

McVeigh had been filmed by a security camera at a nearby McDonald's 24 minutes before the time stamped on the rental agreement, wearing clothes that did not match either of the men seen at Elliott's. There is also no plausible explanation of how he travelled the mile and a quarter from McDonald's to the rental agency, carless and alone as he claims, without getting soaked in the rain. The three people interviewed agreed John Does 1 and 2 were dry.

According to Stephen Jones, who has seen the interview transcripts, it took 44 days for the FBI to convince the car rental agency owner that John Doe 1 was Timothy McVeigh. And in the end they did not dare put him on the witness stand, for fear of what might happen under cross-examination. Jones, a man widely criticised - notably by his client - for his apparently gutless handling of the trial, could have called many of the eyewitnesses himself if he had wanted. His problem was that for all the evidence he could have presented about John Doe 2 (not to mention Does 3, 4, 5 and up), few if any of the witnesses would have proved exculpatory to McVeigh.

The one person he did call, Daina Bradley, had seen a second man from inside the Murrah building; her credibility, however, was demolished under cross-examination when she admitted a history of mental problems and continuing trauma after the bombing, in which she lost two children and her mother and had to have her right leg hacked off without anaesthetic by rescue workers after it became trapped in rubble.

Jones was more successful in attacking the internal logic of the government's lone-bomber theory. It beggared belief that McVeigh would drive the Ryder truck several hundred miles with the bomb fully loaded, he argued, particularly given the history of car bombers inadvertently blowing themselves up in Northern Ireland. McVeigh himself had a close call with a car crash in Michigan in December 1994, when he was carrying detonators in his car; he swore at the time to be more careful around explosives.

And then there was the mystery of the extra leg. The rescue teams who cleaned up after the bombing had found nine severed left legs, but only eight bodies to match them with. The government's medical examiner confirmed this in court. Moreover, the state of the extra leg was consistent with someone who had been extremely close to the source of the blast. Who could it belong to? Jones is convinced it must be one of the bombers.

In the course of his research he talked to the former chief state pathologist for Northern Ireland who had conducted more than 2,500 autopsies on bombing victims, and told him: "In the Western world, there is no such thing as an unclaimed innocent victim. Everyone gets claimed, sooner or later, unless there is a particular reason not to."

There are other questions for which the official account has no satisfactory answer, notably how McVeigh managed to support himself financially after he stopped regular paid work in late 1992. The bomb itself was not particularly expensive, no more than a few thousand dollars once you consider that the Tovex and blasting caps were stolen from a quarry in Kansas. But McVeigh led an extraordinarily itinerant lifestyle, particularly after November 1994, when he barely stopped moving, frantically criss-crossing the country in his car and staying in motels at almost every turn. Somehow, he paid cash for everything.

After he left the army, McVeigh actually fell heavily in debt, partly because of his habit of gambling on the Buffalo Bills football team. Terry Nichols, meanwhile, accumulated about $50,000 in credit- card bills by mid-1993. These are not problems that can be explained away by the pair's occasional selling activities at gun shows; numerous gun-show participants have testified they were usually so broke, they could not afford an exhibition table.

According to the official version of the bombing, the major source of funding was a November 1994 robbery at the Arkansas home of Roger Moore, a gun collector and self-made businessman who knew McVeigh from the gun- show circuit. Although McVeigh did not commit the robbery himself - who did is a source of some mystery - he has admitted being behind it, netting $8,700 in cash and an estimated $60,000 in silver bars, gold bullion, jewellery and firearms.

It is not clear, however, how much of this loot was put to use. Some of the weapons were later sold, but much of the rest was recovered untouched from a storage locker in Las Vegas where it had been stashed by Nichols. The Moore robbery only helps to account for one of several plane trips Nichols made to his mail-order bride's home in the Philippines, for which he paid cash every time. And it does not begin to explain how McVeigh - to take one example of many - repaid a $4,000 debt to his father in $100 bills a full year before the robbery.

From the start, there has been no lack of conspiracy theories about the Oklahoma City bombing, many of them absurd and many displaying the same government-hating bias that drove McVeigh. There was one claim that the bombing was a federal sting operation gone horribly wrong; another that there were explosive packs strapped to the internal pillars of the Murrah building, timed to go off at the same time as the fertiliser bomb. There is no credible evidence for either claim.

Much serious inquiry focused instead on Elohim City, a heavily armed religious compound in a remote part of eastern Oklahoma with strong links to a group of Aryan supremacists who had previously plotted to blow up the Murrah building in the 1980s. By macabre coincidence, one of those original conspirators, Richard Wayne Snell, was executed in Arkansas on the day of the bombing - for the murder of a state trooper and a pawnbroker whose name sounded Jewish - and his body brought to Elohim City the next day for burial.

It emerged that a secret informant for the federal Bureau of Alcohol, Tobacco and Firearms (ATF), reporting from inside Elohim City, told her handlers in late 1994 that at least two residents, a formidable White Aryan Resistance leader called Dennis Mahon and a German ex-serviceman called Andreas Strassmeir, had talked about blowing up a government installation and mentioned the Murrah building as a possible target. She accompanied members of the commune on one of three field trips to Oklahoma City in late 1994 and early 1995. She also reported sightings of McVeigh at the compound under the pseudonym Tim Tuttle.

To many people, the link seemed irresistible, not least because one Elohim City resident, Michael Brescia, bore a striking resemblance to the composite sketch of John Doe 2, right down to the tattoo on his upper left arm. But nobody - not the few journalists who got into Elohim City and not, one presumes, the FBI - could quite join all the dots. McVeigh admitted having met Andreas Strassmeir at a gun show in Tulsa in March 1993, and is on record as having made a brief phone call to Elohim City two weeks before the bombing, a call he now says was a part of an unsuccessful attempt to find a place to hide after 19 April.

That, on its own, didn't prove much. There were reports of many other contacts and visits, but even these did not establish, without further corroboration, more than an association between like- minded people.

The ATF informant, Carol Howe, had her credibility hammered as the FBI accused her of mental instability and put her on trial for harbouring her own bomb plots. Many of the accusations against her were grossly unfair, seemingly the result of attempts ahead of the McVeigh trial to pour cold water on the whole Elohim City connection; she was acquitted of the charges against her in less than a week. Still, there are grounds for thinking she embroidered some of the reports she filed after the bombing to justify her hastily increased government pay cheque. Those who have met her in recent years have described her as "a walking crackpipe" - armed, paranoid, and living under a variety of aliases in ever-changing locations for fear of reprisals from the people she snitched on.

In short, after a burst of investigative energy in the first couple of years after the bombing, the conspiracy trail appeared to go cold. But that was before people had heard of the Aryan Republican Army. Over a two-year period, from late 1993 until the end of 1995, a small band of robbers managed to hold up 22 banks across the American Midwest. It was an unfailingly colourful affair. The ringleader, Pete Langan, would shout "No alarms, no hostages!" as he leapfrogged over the tellers' desks and emptied their cash drawers. His main associate, Richard "Wild Bill" Guthrie, would yell phrases in Arabic, or Spanish, or Serbo-Croat, just to rattle everyone.

The team would snatch and run, making sure they were in and out in under 60 seconds. To sow confusion, they liked to leave a hoax explosive device on the scene, using real gunpowder and plenty of scary-looking wires to divert police attention. If possible, they used two getaway vehicles - the "drop car" they would abandon, plus their own Ford van they nicknamed "the Blitzenvagon". Sometimes, a fake bomb would be left in the drop car, too. They liked to wear toyshop masks of politicians, a touch straight out of the 1991 Hollywood heist movie Point Break. They frequently donned costumes, wigs and make-up.

They never failed to display a humorous sense of occasion. One Christmas, Langan dressed up as Santa and announced: "Ho ho ho, get down on the floor." One Easter, the fake explosive came in a little basket with Easter treats in it. Whenever they took off from an establishment, they would shout out: "Bank you very much!" Before they were caught, the bankrobbers netted about $250,000 and, perhaps more remarkably, gave away almost nothing about their identities or their safe house in Pittsburg. Guthrie proved to be the weak link in the chain, first being cut out of new jobs because he was deemed too wild - he thought, for example, it was great fun to taunt law enforcement officials with announcements of the gang's exploits - and then betrayed to the police by a friend turned informer. Guthrie, in turn, squealed on the others.

When the FBI came for Langan, they opened fire on him in his truck (they thought, wrongly, that he had fired first), spraying him with more than 50 bullets but miraculously missing every time. They later discovered that he had shaved his pubic hair and painted his toenails pink. Yes, the ringleaders of the Midwest bank robbery gang were closet transvestites - and that was only the first of many secrets to be learned about them.

They were also virulent anti-government white supremacists, for whom bank robbery was merely a means to a much more ambitious end. "Make the land ungovernable - that's what we want to do," Langan, aka Commander Pedro, had said in an extraordinary recruitment video made at the height of the gang's success in early 1995.

Both Langan and Guthrie had frequented the Aryan Nations and other right- wing hate groups. They modelled themselves on the Order, the underground guerrilla movement that stole $3.8m from an armoured truck in California and killed the Jewish talk-radio host Alan Berg in Denver in the early 1980s before going out in a blaze of gunfire in an FBI siege on Whidbey Island, near Seattle. They were fond of a propaganda novel called The Turner Diaries, written by the leader of the neo-Nazi National Alliance, in which a gang of revolutionaries blows up the FBI's Washington headquarters with a truck bomb. (The Turner Diaries was Tim McVeigh's favourite book, too.)

They had also read an influential neo-Nazi essay espousing the notion of "leaderless resistance" - developing a guerrilla-style cell structure in which nobody knew more than was strictly necessary and each element worked as independently as possible of the others. The Aryan Republican Army (ARA) was born when Langan and Guthrie, after their first few successful robberies, went to see Mark Thomas, a Ku-Klux- Klan leader in western Pennsylvania, in search of new recruits. Thomas, in turn, put them in touch with Scott Stedeford and Kevin McCarthy, two young Philadelphia skinheads who had played together in a Nazi punk band called Cyanide. Soon, with HK-91 assault weapons packed into their old guitar cases, they formed a revolutionary cell whose aims stretched far beyond bank robbery.

"Mark... believed that if the Company [a nickname for the ARA inspired by the CIA] attacked various places like utilities, railways, communications and even government installations, [then] ARA would become a force that the government would have to reckon with," Guthrie wrote in a 300-page handwritten memoir that he completed in prison before hanging himself with a bedsheet in July 1996. Bob Mathews, the inspirational leader of the Order, had advocated something very similar a decade earlier.

The members of the ARA knew each other only by their first names, or by noms de guerre like Pedro (Langan), Pavell (Guthrie), Tuco (Stedeford) and Newt (McCarthy). They gathered at the safe house in Kansas, and later at a second one in Columbus, Ohio, discussing the coming revolution as they divided up the bank spoils between themselves and a Company fund set aside to finance other guerrilla cells.

In the recruitment video, a weird Pythonesque assemblage of goose- stepping, semi-humorous drunken rants, spoof commercial breaks and racist invective entitled "The Aryan Republican Army Presents: The Armed Struggle Underground", a masked Commander Pedro shows off his arsenal of weaponry and pulls wads of banknotes out of pickle jars on his desk, all the while declaring war on the "federal whores". "Linger on this continent at your own peril," he says. "We have endeavoured to keep collateral damage and civilian casualties to a minimum... but, as in all wars, some innocents shall suffer. So be it."

The full significance of these words did not become clear for several years. The leading academic researcher on the ARA, an Indiana State University criminologist called Mark Hamm, failed to see any meaningful link to McVeigh when he began writing about the group in 1997, even though his previous book had been about the Oklahoma City bomb and its roots in far-right political ideology.

"I thought I was done with the bombing and was now writing about a gang of bank robbers," Hamm said. But then something decidedly odd happened. In August last year, shortly before his book on the ARA was due to go to press, he sent the manuscript to Pete Langan at the Supermax prison in Florence, Colorado, where he is serving life without parole. Langan, who has consistently denied all involvement in the Oklahoma bomb and denounced the killing of innocent civilians, phoned him to say the book was fine as far as it went but was missing a crucial element - the work of an Oklahoma journalist called JD Cash.

Cash is a name that anybody who looks into the Oklahoma City bombing runs into sooner or later. A former banker and property manager, he was inspired to go into journalism by a friend who was killed in the Murrah building and has devoted the last six years to a single subject, the bombing and the possible conspiracy behind it. His newspaper, the McCurtain Gazette, serves a tiny town in south- eastern Oklahoma called Idabel (pop: 6,500) and yet has somehow managed to break story after story on the bombing. ("Where the hell's Idabel?" one Justice Department official was overheard exclaiming after one spectacular leak of FBI documents in 1996.)

Despite mutterings about some kind of political agenda, Cash's information has proved unnervingly correct on numerous occasions. He got out in front of the story by forming a strategic alliance with McVeigh's defence team: he broke the ice for Stephen Jones's investigators with a number of key witnesses who were otherwise reluctant to talk to representatives of an indicted killer, and in return he got to see several confidential trial documents. He found out about McVeigh's 5 April phone call to Elohim City.

He discovered Carol Howe and revealed that she had been a government informer. He was also convinced - and this is why Langan's tip was important - that the ARA was deeply involved in the bombing. "Like many people, I had been a bit sceptical about Cash's work," Hamm explained. "But when the main character you're writing about tells you to go look somewhere, you go look." One of the first things Hamm did was to take the detailed timeline he had developed of the ARA's activities and overlay it with an equally detailed timeline on McVeigh, adding bits of Cash's research as he went.

The result was akin to placing layers of the same film animation frame on top of each other - a remarkable series of concurrent and complementary events that fit so snugly together it became hard, if not impossible, to regard them as simple coincidence. Much of the activity centred on the four-state area comprising Kansas, Missouri, Arkansas and Oklahoma, an area known historically as a hotbed of tax revolts, white supremacist Christian sects, Ku-Klux-Klan chapters and overt hostility to the federal government.

On 11-12 October 1993, McVeigh, Nichols and the ARA were all in Fayetteville, Arkansas. The ARA was there on an unsuccessful mission to rob an armoured truck in Springdale, 20 miles to the north; Guthrie wrote in his memoir that the job needed "at least one additional participant" and McVeigh had worked as an armoured truck driver. Fayetteville was close to Elohim City (McVeigh received a speeding ticket just four miles from the compound), and also to the home of the leader of the Arkansas Knights of the Ku-Klux- Klan who had met and possibly inducted both McVeigh and Guthrie a year earlier.

On 20 October, McVeigh wrote to his sister Jennifer saying he had met "a network of friends who share [my] beliefs". At the time of nine out of the ARA's first 10 bank jobs, which began around this time, McVeigh's whereabouts are unaccounted for. (The one exception was a robbery in Missouri in July 1994, when McVeigh was with his ailing grandfather in New York state.)

On Christmas Eve, 1993, McVeigh alluded to bank robberies in another letter to his sister: "The Federal Reserve and the banks are the real criminals, so where is the crime in getting even? I guess if I reflect, it's sort of a Robin Hood thing..." About a year later, according to Jennifer's testimony to the FBI, McVeigh produced a wad of $100 notes he claimed to have received as payment for helping to organise a bank robbery; he gave her three of them, asking her to exchange them for clean money. Shortly afterwards, Jennifer paid $25,000 in cash for a spanking new Jeep Cherokee.

On 12 September 1994, McVeigh checked into a hotel in Vian, Oklahoma, a 20-minute drive from Elohim City. He was later seen on the compound's gun range with Dennis Mahon, a close friend of Mark Thomas. Elohim City's residents at that time included two of the newer ARA members, Kevin McCarthy and Michael Brescia, the man later suspected of being John Doe 2, who also happened to be another Cyanide band member.

On 10-11 December 1994, McVeigh, McCarthy and Stedeford all attended the same gun show in Overland Park, a Kansas City suburb where Langan kept a residence for his cross-dressing escapades. At around this time, McVeigh wrote to his sister about "something big" that he was planning and added: "I have also been working and establishing a network of friends so that if someone does start looking for me, I will know ahead of time and be warned. If that tip ever comes (I have `ears' all over the country) that's when I disappear or go completely underground." Langan and Guthrie, both wanted for a long catalogue of past crimes, had been successfully living beyond the reach of the law for two years.

At the beginning of February 1995, there was another startling series of coincidences. McVeigh broke off a gunshow tour of Kansas with Nichols and headed for Arizona. The ARA, who had been in Kansas at their safe house, also dropped everything and went to Arizona - the first time they had ever left the Midwest. Ostensibly, according to Guthrie's memoir, the idea was to find an armoured truck to rob in a Phoenix suburb, although no such robbery ever took place.

The record of McVeigh's telephone card shows he called a few armoured truck companies in Arizona before starting his journey west. Both McVeigh and the ARA spent much of the next month and a half in Arizona. When criminologist Mark Hamm saw the pattern, he was flabbergasted. "Are we to assume that these people came together by happenstance?" he said. "So many random coincidences have to be statistically impossible. There must have been some larger card at play."

The pattern only grew stronger once he added in the extraordinary legwork put in by the journalist JD Cash and a handful of other dogged reporters and investigators. These people had followed McVeigh's every step, quizzing anyone who might have seen him or had dealings with him, and painstakingly matched one eyewitness account against another to build up a fuller picture. Cash even passed himself off as a far-right activist for a while, accepting an invitation to speak at a neo-Nazi rally and allowing his work to appear on websites operated by militia groups. The purpose of this subterfuge was to gain access to individuals like informant Carol Howe, Dennis Mahon and the patriarch of Elohim City.

It was an investigative strategy fraught with personal risk, particularly after Cash told his extremist contacts in 1997 that he was not one of them after all. But it also paid off handsomely, netting Cash a trove of valuable new information that Hamm now considers to be at least 90 per cent reliable. For the past six months, the two men have pooled their information and found agreement on almost every key point.

The more Hamm looked at it, the involvement of the ARA was the only plausible explanation for the bombing. Looking to Elohim City for the key to the mystery had been only half-right, because these people were not based in any one place, did not communicate anything except on a strict "need- to-know" basis, and barely knew each others' names. They moved constantly across the country under a variety of aliases, operating entirely in cash. According to the scheme laid out above, McVeigh and ARA had time to develop a history together. They had money to fund their ambitions. They also had the skills necessary to carry out the bombing - skills that McVeigh lacked on his own. Guthrie, for example, had been trained in explosives handling during his time as a Navy Seal (he was expelled for painting a swastika on a ship).

Langan was a master of decoy, disguise and complex planning. McVeigh, by contrast, knew about weapons and armoured cars and trucks but little else. The notion, put forward in the book American Terrorist, that he taught himself bomb-making out of books does not pass muster with military experts. "In criminology, there is a theory that the two elements you need to pull off a major crime are ideology and skill. I'd add to that and say you also need organisation and fanatical dedication," Hamm said.

Ideology was something shared by everyone, their anti-government rage sharpened by the deaths of more than 80 residents at the Branch Davidian religious compound near Waco, Texas, at the apocalyptic climax to a 51- day law enforcement siege that took place two years to the day before the Oklahoma bombing. The other three elements, however, were not apparent in McVeigh's official co-conspirators. Neither Nichols nor Fortier, the drug-addicted friend from Arizona whose trial testimony, following a plea bargain, proved crucial in securing McVeigh's conviction, had the necessary skills or experience.

Both wavered in their commitment to the bombing several times, prompting McVeigh, according to Fortier's account, to storm off at one point in search of "some manly friends". A rich irony this: could he possibly have meant the transvestite Pete Langan? The ARA, on the other hand, experienced no wavering, at least during the period in question. Hamm now believes the ARA financed several cells, some or all of which could have been involved in the Oklahoma City bombing: McVeigh's operational cell, including Nichols and Fortier, whose key role was not so much to carry out the bombing as to take the fall for it if necessary; a security and fund-raising cell, essentially the hard core of the ARA; a training cell, led by Andreas Strassmeir, whose "platoon- sized groups" of militia trainees were noted in a May 1995 FBI report and prompted the federal authorities to think about a Waco-stye raid on Elohim City on two separate occasions; a bomb-building cell, and possibly a leadership cell, co-ordinated by people such as Mark Thomas and Dennis Mahon who had direct links to the elder statesmen of the far-right movement.

Why did none of this come out at the ARA trials? Why didn't the FBI, which had access to all the information, actively pursue the links to the Oklahoma bombing? The answer, as in the McVeigh trial, was largely to do with courtroom strategy. To be sure of convicting the surviving defendants - Langan, Stedeford, McCarthy, Brescia and Thomas - they persuaded two of them, McCarthy and Thomas, to testify against the others in exchange for reduced sentences.

That, in turn, left them with a dilemma. If they introduced the idea of complicity in the bombing, they risked tainting the credibility of the two witnesses to such a degree that the prosecution might end up with no convictions for the bank robberies at all. And that, in turn, might jeopardise the prospects of pressing bomb conspiracy charges in the future. Was the risk worth it?

According to a confidential source who was involved, the FBI was initially very active in pursuing the bombing angle but then dropped all mention of it once the two witnesses entered the government protection programme. One can only speculate exactly why the feds made that decision, but embarrassment must have played some role. Embarrassment to admit they had some idea about McVeigh's possible accomplices after all. Embarrassment, too, over the fact that in 1992 the Secret Service let Langan out of prison following a Pizza Hut robbery in Georgia and paid for him to go home to Cincinnati on the understanding he would lead the authorities to Guthrie, who had been overheard threatening to assassinate President Bush.

Langan strung the government along for six weeks before vanishing, with Guthrie, to begin a new underground life of anti-government subversion. In his memoir, Guthrie dismisses Cash's early allegations of a link between McVeigh and the ARA as "flambeed gobbledygook", but he also describes the Oklahoma bombing as "the beginning of what lies [ahead]." He wrote: "Simply put, within 10 years it's my opinion that this country will resemble Sarajevo."

Here's one more intriguing titbit. In his witness statement to the FBI, Guthrie named one of the ARA bank robbery gang as an individual named "Tim". The FBI insists that "Tim" is a nickname for Brescia. (He wasn't arrested until six months after the others.) But isn't the FBI avoiding the more obvious conclusion - that "Tim" refers to McVeigh?

Nobody knows exactly what McVeigh and the ARA got up to in Arizona in February and March 1995, but something else was going on that may have been directly related to them. Two survivalists called Steve Colbern and Dennis Malzac began experimenting with detonators and small explosives in the desert outside Kingman, the town where Michael Fortier lived and McVeigh had taken up temporary residence.

McVeigh had heard about Colbern from Roger Moore, the businessman robbed in Arkansas three months previously, and had written him a recruitment letter at the end of November 1994 that was never received: a water company employee found it strapped to the leg of a transmission tower on the Arizona- California border. "I'm not looking for talkers, I'm looking for fighters," McVeigh had written. "And if you are a fed, think twice."

On 21 February, a large ammonium nitrate bomb exploded outside the home of one Rocky McPeak, just outside Kingman, apparently the work of Colbern, Malzac and a local loan shark called Clark Vollmer. McPeak later testified to an Oklahoma grand jury investigation that when he went to Vollmer's home the next day to confront him about it, he found McVeigh and another unidentified man there. Was the McPeak incident a trial run for Oklahoma City, with McVeigh taking lessons in bomb-building?

During this time, McVeigh was described by several people as agitated to the point of paranoia, leading to speculation that he was strung out on crystal meth. By his own admission, he had tried the drug before, and crystal meth does not lend itself easily to occasional use. It is noted for the short-term sense of empowerment it gives its users, and its tendency to instill paranoid delusions.

On several occasions, a stream of people was seen flowing in and out of McVeigh's motel room, and in one establishment his guests made so much noise that he was thrown out. This was not the behaviour of a lone-wolf terrorist mastermind.

As 19 April approached, the number of coincidences and bizarre sightings multiplied. An unusual flag previously seen in the ARA's propaganda video, featuring a coiled snake against a white background, appeared outside Michael Fortier's Kingman home. In February, Guthrie bought a 1970s-era Chevy pickup, the same make and era as the vehicle seen so often in Oklahoma City on the morning of the bombing. On 1 April, a pickup matching its description was seen outside Terry Nichols' house in Herington, Kansas.

Also on 1 April, Stedeford, McCarthy and Thomas went to Elohim City, ostensibly to wait for the funeral of Richard Snell following his execution in Arkansas. But they, along with Dennis Mahon, left again a few days before the funeral had taken place. Thomas went to Pennsylvania and Mahon to Illinois, possibly to establish alibis for the bombing. The whereabouts of the other two men on 19 April are unknown.

Then, as first reported in the Denver Post, there were the anomalous sightings of yellow moving trucks around Kansas and Oklahoma, well before the Ryder was rented from Elliott's on 17 April. As early as 8 April, one was seen parked outside the Lady Godiva strip club in Tulsa, at the same time as three men, later identified as McVeigh, Strassmeir and Brescia, were inside. A showgirl, captured on a dressing-room security video, told her fellow strippers that one of the three had boasted to her: "On 19 April 1995, you'll remember me for the rest of your life."

Another yellow truck, along with a Chevy pickup, turned up on 10 April at Geary Lake in Kansas, not far from Nichols's house. The truck was seen again repeatedly over the next week, both at the lake, where McVeigh claimed he mixed the bomb with Nichols, and at the Dreamland Motel in Junction City, where McVeigh checked in on the 14th.

Were the witnesses imagining things, or was there a deliberate strategy to try to confuse everyone? Mark Hamm argues vigorously for the latter, pointing to the ARA's track record of switch cars, disguises and very careful staking of their territory before every crime. If he is right, then who exactly was in Oklahoma City on 19 April? That is a tough question, and no serious researcher claims to have anything close to a definitive answer. Michael Brescia, with his strong resemblance to John Doe 2, is a leading candidate. So too is Pete Langan, whose likeness was captured with remarkable accuracy in an artist's sketch of a man seen by a loading bay worker in downtown Oklahoma City who signalled in vain to the Ryder truck to pull into his slot as it approached.

As for the others, one can only guess. Hamm describes the left leg recovered without a body as "The Phantom", a member of the bombing team whose identity has never even been hinted at. "I'm not saying I have all the answers. I don't have any smoking gun. As a criminologist I look for patterns and develop theories. I don't necessarily have hard evidence that can stand up in court."

That probably also summarises the way government investigators feel about their flawed efforts. For all the bruising disappointments and public distortions of the past six years, the FBI can at least console itself that most, if not all, of the suspected conspirators are out of harm's way - for the moment. Guthrie is dead, and Langan is in prison for life. But Brescia got only six years, and Thomas and McCarthy - who will be under government supervision as protected witnesses when they are released - were given eight and five respectively. Stedeford got 20 years, but could well be out sooner. And that's not to mention those suspects who have escaped the judicial heat altogether: Dennis Mahon, who still lives in Tulsa, and Andreas Strassmeir, who returned to Germany nine months after the bombing.

It remains to be seen how the public reacts once these findings receive a wide airing. Hamm's book - now heavily rewritten - will be published in the autumn. Will Americans accept his conclusions and, if so, will they find the justice system at fault?

The man best placed to fill in the gaps and provide some concrete answers is, of course, McVeigh himself. He has given little away in his correspondence and in media interviews, beyond what he told the two Buffalo journalists for their book. In a few days, assuming that here is no dramatic 11th-hour reversal, he will be strapped into a mounted stretcher at the US penitentiary in Terre Haute, Indiana, and become the first federal prisoner to be put to death in almost 40 years.

Nobody doubts his guilt, which he now freely confesses. Everyone agrees that he is utterly unrepentant. John Ashcroft, President Bush's ultra- conservative attorney general, would have us believe that his death, which is to be broadcast on closed-circuit television to the victims and their relatives in Oklahoma City, will enable the country to achieve "closure."

Shouldn't we worry, though, that the networks of guerrilla activism that gave rise to the bombing may be very far from closed? Aren't there a few things the world's most notorious mass murderer should tell us before he is allowed to depart this life and descend into silence for ever?

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