From the Washington Post:
A neuroscience faculty member, who declined to be identified because of privacy concerns, described Holmes as “very quiet, strangely quiet in class,” and said he seemed “socially off.” Although Holmes got weak scores on the comprehensive exams last semester, the educator said, the school’s staff wasn’t going to toss him out. Instead, they planned to give him remedial instruction and perhaps put him on academic probation.
...Michael Welner, a forensic psychiatrist who, as chairman of the Forensic Panel of New York City, has studied and testified about mass shootings, said these cases invariably feature a person who is highly paranoid, resents the broader community and decides to kill out of a desire to achieve notoriety.
“Some are so paranoid that they’re psychotic. Others are paranoid in a generally resentful way but have no significant psychiatric illness. But you have to hate everyone in order to kill anyone,” Welner said.
“The threshold that the mass shooter crosses is one in which he decides that his righteous indignation and entitlement to destroy is more important than the life of any random person that he might kill.”
James Eagan Holmes held in Colorado shooting - The Washington Post