In emails addressed to himself and his wife, he said he wanted to kill at least 200 students and the assistant principal at University High School in Irvine.
In one email, the German national said he wanted to buy 12 machine guns, burn down the high school and rape two female staffers before killing himself at William R. Mason Regional Park, according to court documents.
Reinscheid's son killed himself in that park in March.
Irvine police originally arrested Reinscheid July 24 after they allegedly found him in Mason Park, crouching in a bush with stacks of newspapers doused with lighter fluid, court documents show.
He was released on bail that day. Police later found the incriminating emails and again arrested the professor three days later.
Deputy District Attorney Andrew Katz said Reinscheid crafted a new will July 27, the day he was arrested on suspicion of multiple arsons.
"If this was a case of just threats alone, obviously we wouldn't be here," Katz said during Reinscheid's arraignment in the Harbor Justice Center in Newport Beach. "He's acting out on what he started."
Katz likened Reinscheid's fantasies to those of the Columbine and Aurora shooters and said Reinscheid didn't value his own life.
"This is a man ready to check out on life," Katz said.
Reinscheid's attorney, Ron Cordova, said his client was a man fueled by psychotropic drugs and alcohol.
"There is no physical evidence to corroborate that theory," he said. "Such homicidal ideation is common, and it's common in normal people."
He described Reinscheid's letter writing as a therapeutic activity in which his client was "purging" and "cleansing" himself of such thoughts.
"He was bridled by that which a psychopath does not have," Cordova said of an email in which Reinscheid said he wasn't strong enough to carry out his plan.
Reinscheid, dressed in an orange jail jumpsuit, nodded his head as he spoke to his attorney from the courtroom's holding cell.
Reinscheid is next expected in court Sept. 6.