Omar Mateen showed extreme signs of aggression years before his deadly attack.
TMZ has learned when Mateen was just 14 years old, he had a violent outburst in the middle of a math class. According to docs, without any provocation, Mateen lunged at a classmate ... repeatedly striking him in the head. Mateen continued the beating until a teacher physically intervened.
Mateen was charged with criminal battery. He was also charged with the crime of disruption of educational institutions. He was placed on probation, sentenced to 30 hours of community service and ordered to write a letter apologizing to the victim.
Mateen was also required to tour a local jail and boot camp ... a so-called "scared straight" sentence.