Investigators said Rainer Reinscheid, 48, emailed his wife detailing plans to burn down University High School in Irvine and then kill school officials and students.
Reinscheid's 14-year-old son committed suicide earlier this year after being disciplined by the school for allegedly stealing from a campus store.
A judge on Wednesday ordered Reinscheid to remain in custody without bail.
"There is a substantial likelihood that he would carry out these threats if he's released. He has done the legwork. He has done the homework. He has the information necessary to carry out his plan," said Judge Karen Robinson.