Authorities say they found the emails on the cellphone of Rainer Reinscheid, 48, who is being held without bail.
One of alleged emails reads: "I have dreams about going to Uni High and setting the place on fire, burning down every single building and then killing myself in the same place where Claas died.
"I am thinking about getting a dozen machine guns, then going to the school and shooting down that *** vice-principal, then the principal and the stupid counselor lady, then I will shoot at least 200 students before killing myself..."
Reinscheid's 14-year-old son, Claas, committed suicide at Mason Park Preserve five months ago after he was disciplined by the vice principal at school for stealing a small item from the student store.
In another email, Reinscheid allegedly wrote: "I will find this vice-principal and find out where he lives, then I will wait for him and kill him. I will force him to tie a rope around his neck and if he is too coward, I will do it for him, in front of his wife and children."
According to authorities Reinscheid did set a fire at the home of the school's vice principal as well as at University High. Reinscheid was arrested on July 24 at Mason Park while allegedly trying to start a fire.
Reinscheid posted bail but was re-arrested three days later after authorities found the emails with the details of his alleged mass-murder plot.
In a statement, Claas's mother, now divorced from Reinscheid, told ABC News: "You know, this guy has been so successful with everything, everything...until his son took his life and he didn't know how to deal with it. He's completely going crazy."
Reinscheid, an associate professor of pharmacology science of 12 years, was charged with five counts of arson, one count of attempted arson and a misdemeanor count of resisting or obstructing a police officer.
Investigators said they believe Reinscheid acted alone and was the only suspect in the case. None of the fires caused serious damage.
At Reinscheid's first court appearance Tuesday, prosecutors said they planned to ask a judge that he be denied bail given the violence detailed in the emails. His arraignment was continued until August 8.