Rainer Klaus Reinscheid already faces nine felony charges for allegedly setting fires at University High School, Mason Park Preserve and a school administrator's home.
The 49-year-old has pleaded not guilty. Reinscheid's teenaged son committed suicide after being disciplined at school.
On Thursday morning, Reinscheid will be charged with setting another fire last summer.
Investigators said they discovered emails by Reinscheid detailing plans to buy guns, burn down the high school and murder students and administrators.