He also spent more than three months at a wilderness survival camp in Utah for troubled teens.
Katz was treated for schizophrenia with anti-psychotic and anti-depressant drugs, according to the divorce documents.
"David would go days without bathing, would play video games until 4 a.m. on school nights, would walk around the house in circles," the judge who heard the divorce case said.
Once, when his mother hid his game controller, he "punched a hole in her bedroom door." Sometimes he'd "curl up in a ball and sob."
Kevin Osai, who attended high school and the University of Maryland with Katz, says he had an explosive temper.
“If he got upset he would get vehement, very upset, all at once,” he told Inside Edition. “He was seeing the school counselor fairly often, pretty much throughout all of high school."
Sunday's Jacksonville shooting spree is shedding light on the world of esports, which is a $1 billion industry.
More than 360 million people worldwide tuned in to an online gaming event called League of Legends, which streamed live last year. The audience for the online event was three times as that of the Super Bowl.
InsideEdition.com recently profiled gamers in Texas, who practice for 10 hours a day. They also work out in the gym, just like professional athletes, and stick to strict diets.
About 50 colleges offer esports scholarships to students, many of whom hope to strike it rich.