A 911 call from a student at the University of Central Florida and a quick response by campus police may have prevented a mass murder.

Campus police said Monday that 30-year-old James Oliver Seevakumaran -- who shot himself in the head as officers arrived, before any other students were hurt -- was heavily armed with two guns, hundreds of rounds of ammunition, a backpack filled with explosives and a plan to attack other students as they fled the seven-story dorm where he lived.

Seevakumaran's roommate, who hid in a bathroom after Seevakumaran pointed a gun at him, called authorities about the incident, UCF Police Chief Richard Beary said.

Around the same time, Seevakumaran pulled a fire alarm, apparently to get other students out in the open, the police chief said.

Police officers responded to the dorm within three minutes of the first call.

"His timeline got off," Beary said. "We think the rapid response of law enforcement may have changed his ability to think quickly on his feet."

In his room, investigators found four makeshift explosive devices in a backpack, a .45-caliber handgun, a .22-caliber tactical rifle, and a couple hundred rounds of ammunition, police said. Beary said it appears his weapons and ammunition purchases began in February locally in Orlando.

Antonio Whitehead, 21, said he heard the fire alarm go off in the dorm and thought it was a routine event.

"All of a sudden, I felt the crowd move a little faster. And a police officer with a machine gun or something told everyone to start moving a lot faster," he said.

Some 500 students were evacuated from the building just after midnight, unaware how narrowly they had escaped what could have been another Virginia Tech-style bloodbath. Morning classes were canceled, but most campus operations resumed around noon.

"It could have been a very bad day here for everybody. All things considered, I think we were very blessed here at the University of Central Florida," Beary said. "One shooting is bad enough. Multiples would have been unthinkable. So, anybody armed with this type of weapon and ammunition could have hurt a lot of people here, particularly in a crowded area as people were evacuating."

Roommates told detectives that while Seevakumaran showed some anti-social tendencies, he had never expressed any violent behavior. The business major, who held a job at an on-campus sushi restaurant, had never been seen by university counselors and had no disciplinary problems with other students, said university spokesman Grant Heston.

Police shed no light on a motive, but Heston said that the school had been in the process of removing Seevakumaran from the dormitory because he hadn't enrolled for the current semester. He had attended the university from 2010 through the fall semester.

Detectives found notes and other writings that indicated Seevakumaran had carefully planned an attack and "laid out a timeline of where he was going to be and what he was going to do," Beary said.

The Associated Press contributed to this report

