"I just slammed the door," the roommate told CNN's Anderson Cooper on Tuesday night. "I was not going to let him shoot me."
Babakhani said he first locked his door, hid behind a chest of drawers, then got behind a cabinet in the bathroom and called 911.
"My roommate just pulled a fire alarm, and he's got a gun out," he told the dispatcher.
While realizing Seevakumaran was far from a rah-rah college student, Babakhani didn't consider him a threat. But in retrospect, the roommate did say he believed Seevakumaran was having money problems from having had his hours cut at a job and that, with seemingly no one to turn to, he might have like he was "in a corner."
"I just thought that he kept to himself a lot," he said, according to audio posted on the Knightly News website. "I just thought he was a quiet, introverted person."
'I don't think you do that as a joke'
Whatever his relatives and acquaintances thought of him, police said they believe that Seevakumaran had devious plans of his own.
Waiting for him in the university mail room were two 22-round magazine clips for his semi-automatic rifle, a sling for that weapon, and a training DVD on how to use its laser and shoot it, authorities discovered Tuesday.
This is in addition to the ample ammunition -- including drum magazines, one of them found attached to the gun, that can contain 110 bullets each -- that authorities have found. Then there were the bombs, which Beary said he believes Seevakumaran made himself
Seevakumaran likely spent about $1,000 to buy the guns and ammunition in February, suggesting his plan was set in motion as early as then, the police chief said.
Of course, there also was the checklist he'd drawn up -- and largely followed, albeit apparently hours later than he had planned, after scribbling out items such as "get drunk" and "take shower" -- ahead of his death.
"I don't think ... you purchase 1,000 rounds of ammunition" without a plan, Beary said. "I don't think you do that as a joke."
While Seevakumaran is the only one dead, the mere possibility that he would wage an attack has already had an impact.
Dorms were evacuated, classes were canceled, and the UCF campus was shut down. Counselors were in Tower 1 and elsewhere to talk with students coming to grips with the drama.
School authorities couldn't promise that something like this wouldn't happen again, but they did send out more police on patrol to help students feel safe.
"All of us have a role to play in the welfare of our campus," school President John C. Hitt said Tuesday in a statement, "and we will work together to use this experience to make us even more prepared, more alert, and more secure.