(CNN) -- Throw down some drinks at The Mad Hatter bar in Orlando? Check.  Pull the fire alarm, so about 500 students in Tower 1 on the University of Central Florida campus rush outside, together? Done.  Those three words were the last item of James Oliver Seevakumaran's checklist that he made before, authorities say, he would go out with up to 1,000 rounds of ammunition and start shooting, possibly setting off bombs in the process.  It was not crossed off.  Instead of a mass killing early Monday morning, police reported only one fatality: Seevakumaran.  Video released a day later by University of Central Florida police shows the moment officers discovered him. After getting into his suite, they unlocked his room's door and barged in, yelling and with their weapons raised.  It didn't take them long to realize there was no threat. The 30-year-old lay prone on the floor, having killed himself with a handgun.  "All indications are, just like the rest of his life, he was alone," UCF police Chief Richard Beary said Tuesday.  After just more than a day of investigating, authorities have been able to piece together much of what happened. They have seen surveillance video that shows Seevakumaran pulling the alarm, then returning to his room. They recovered weapons and ammunition as well as four homemade bombs and the checklist. They interviewed many who described him as a loner who didn't like to talk to others but wasn't viewed as a threat.  What they don't know is why he did what he did.  "There's no manifesto, there's no documentation," Beary said. "... We have not uncovered anything that would give us a motive or a rationale."  Family calls him 'a loner'  The statement issued Tuesday by Seevakumaran's family, initially to the Sarasota County, Florida, sheriff's office, didn't shed much light on his thinking.  "The family of James Oliver Seevakumaran states that James was a loner and did not have a history of violence," they said.  Evacuated students at the University of Central Florida on Monday wait to return to their dorm rooms.  From fall 2010 through fall 2012, he had been a UCF student. But he was not enrolled for the spring semester, and was in the process of being removed from the dorm room where he lived, school spokesman Grant Heston said.  According to Heston, Seevakumaran was never seen by UCF counselors and had not had any student conduct issues. He had one prior contact with law enforcement -- a traffic arrest in 2006 -- the police chief said.  One of his roommates, Arabo "BK" Babakhani, told the UCF student news organization the Knightly News that Seevakumaran would seemingly make an effort to avoid walking near him, that he wouldn't say anything back when you said hello.  "The only time that he made solid eye contact with me was when he was pulling the gun on me," the roommate said.  That happened as lights were flashing and the alarm was ringing around 12:20 a.m. Monday, inside their suite. Unsure if he could make it to the hallway, Babakhani ran to his room as Seevakumaran raised what he later described as a "large assault gun" in his direction.  "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'  We were left in the dark. Antionette Thompson, evacuated student  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.  CNN's John Couwels, Dana Ford and Marlena Baldacci contributed to this report.
The suspect in an alleged UCF mass killing plot kept a to-do list marking out his steps, though he killed himself before fully executing the plan, police said.