Police is still searching for a motive after a former student armed with a shotgun and three handguns opened fire in a Northern Illinois University lecture hall, killing five people and injuring 16 before shooting himself dead.

The gunman, dressed in a black trench coat and balaclava, fired 48 shots into the geology class at the school's DeKalb campus, school officials and witnesses said. The man purchased the guns legally a week ago.

"It started and ended within a matter of seconds," university Police Chief Donald Grady said at a televised news conference yesterday. "We have no apparent motive."

The gunman, identified as Stephen Kazmierczak, 27, left NIU to attend the University of Illinois. He had been taking medication for an unidentified condition (his father said it was diabetes) although he had stopped and become erratic in the past two weeks, Grady said.

One of every four patients with diabetes experiences clinical depression.

"We are dealing with a disturbed individual who intended to do harm on this campus," NIU President John G. Peters said in a televised press conference this morning. "We did everything we could to ensure the safety of this university, and we are going to continue in that vein."

The attack comes 10 months after a student at Virginia Polytechnic Institute and State University in Blacksburg, Virginia, killed 32 students and teachers before committing suicide in the deadliest shooting rampage in U.S. history.