As police try to find a motive behind the shooting at an Oakland, California college on Monday that left seven dead, new details about the suspected killer reveal that he had been expelled from the institute after being oppressed by fellow students.

One L. Goh, a 43-year-old former student at Oakland’s Oikos University, tells authorities that he had been “mistreated” and “disrespected” by students at the nursing college before eventually being expelled last year. Speaking of the incident in the aftermath, the head of the Oakland Police Department also alleges that anger with the school’s administration may have played a part in the massacre.