The campus had a plan to respond to emergency situations, university President John Peters said during a news conference. University police Chief Don Grady said officers responded within 30 seconds after first alerted to the situation.

The Valentine's Day assault by the shooter, identified as Stephen Kazmierczak, a 27-year-old former Northern Illinois University student, "concluded before we were actually able to enter the building," Grady said.

"We were dealing with a disturbed individual who intended to do harm on this campus," Peters said.

Five people died and 16 others were injured when Kazmierczak fired on the lecturer and students before turning the gun on himself. Officials pulled back on the number dead, blaming a miscommunication between the DeKalb County coroner and a hospital for the higher, incorrect number.

Kazmierczak entered the geology class -- a shotgun, three handguns and ammunition hidden in a guitar case -- walked out on the stage near the instructor and opened fire, Grady said. Two weapons were lawfully purchased.

Kazmierczak had stopped taking medication about two weeks ago, Grady said, declining to say why Kazmierczak was taking the unidentified medicine.

Peters and Grady said nothing was apparent in Kazmierczak's behavior to indicate something like Thursday's shootings would occur.

"We will get through this together as a community," Peters said.

Classes and activities were canceled indefinitely.