Matthew Taylor Coleman, 40, is facing charges of foreign murder in the killings of his 2-year-old son and 10-month-old daughter.
He allegedly confessed to killing his children with a spearfishing gun in Mexico.
Coleman told FBI agents he believed his children were going to grow into monsters so he had to kill them.
It’s unclear how long Coleman was entrenched in the delusion inspired by the QAnanon.
Coleman was booked at the Santa Ana, California, jail early Tuesday morning, according to the affidavit.
QAnon is a collective delusion that a Satan-worshipping cabal of global elites is operating a global child trafficking network.
The belief system has inspired violence and crime in recent years, including an armed standoff at the Hoover Dam and the hijacking of legitimate attempts to fight child sex trafficking, federal officials say.