"Doomsday prophet" Chad Daybell has been found guilty of three murders after a lengthy trial in which jurors heard of his beliefs in "dark spirits" and zombies.
Prosecutors said Daybell, 55, lusted for "money, power and sex" and - together with his lover Lori Vallow - were involved in the deaths of two of her children and his wife Tammy Daybell.
Now after two months of trial, Daybell has been found guilty of murdering Ms Daybell, Joshua 'JJ' Vallow, seven, and Tylee Ryan, 16.
He could now face the death penalty.
Jurors in Ada County, Idaho, returned their verdicts on Thursday.
Sci-fi author Daybell is rumoured to have gathered followers through his Mormon-inspired books about the apocalypse.
The disappearance of the children sparked a months-long search and gripped news audiences across the US.
It comes almost a year after Vallow - who Daybell went on to marry - was jailed for life for the murders of her two children and conspiring to kill Ms Daybell.
What happened to JJ and Tylee?
In September 2019, two children vanished from the city of Rexburg in Idaho.
Months of searching came to nothing - it was not until June 2020 that police found the mutilated remains of JJ and Tylee at a rural property that belonged to Daybell.
JJ's body was wrapped in rubbish bags, his arms bound in front of him with duct tape. Tylee's remains were charred.
Daybell was arrested after the grim discovery.