After the massacre, it was widely believed Harris and Klebold were part of a clique in school called the "Trenchcoat Mafia", a group of misfits in the school who supposedly rebelled against the popular students. This turned out to be untrue, as neither Harris nor Klebold had any affiliation with the group. The pair's aforementioned writings and videos gave insight into their rationale for the shooting. The FBI concluded that Harris was a psychopath, who exhibited a lack of empathy, narcissistic traits and unconstrained aggression. Klebold, however, was concluded to be an angry depressive, who showed low self-esteem, anxiousness and a vengeful attitude toward individuals who he believed had mistreated him. However, neither Harris nor Klebold were formally diagnosed with any mental illnesses prior to the attack.