From the HuffPo:

Those connected to the school, including the founder and several students, said the gunman had studied nursing. He was upset with administrators at the school, and also with several students.

“They disrespected him, laughed at him. They made fun of his lack of English speaking skills. It made him feel isolated compared to the other students,” Jordan said.

The 43-year-old South Korean national had been expelled, possibly for behavioral problems, according to Jordan.

I’m guessing there are more fundamental mental issues at work here.

UPDATE: According to the JoongAng Ilbo (Korean) Goh’s dad told police his son had caught other students cheating during a test, but was ignored when he informed the professor and later ostracized by students. The father then told the JoongAng Ilbo that after the shooting, his son called him and told him that he’d committed the crime 우발적으로 (I hate translating this word, but basically, without planning, sporadically, “it just sort of happened”) after getting angry suddenly, and that several people were hurt.

And then there is this from the Christian Science Monitor:

Oakland Police Chief Howard Jordan told reporters Tuesday that the suspect – a South Korean national, 43-year-old One Goh – had recently been expelled from the university, for his apparent inability to curtail his own anger. He said Goh was being congenial with police interrogators but showed no regret for the murders.

Several students, interviewed on NBC, said that Goh, being from South Korea, didn’t fit in because of the language barrier.

Six of the victims were women, foreign nationals from Nepal, Korea, the Philippines, and Nigeria.

TIME has another profile of the suspected killer.