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.
Police were first alerted when Seevakumaran pulled a gun on one of his roommates who called 911 and holed up in a bathroom, 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.
Associated Press writer Freida Frisaro in Miami contributed to this report.