Police at Northern Illinois University had little time to prevent a former student from shooting and killing five students before killing himself in an attack that lasted just seconds, authorities said Friday.

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Northern Illinois University Police Chief Donald Grady talks about Thursday's campus shooting during a news conference in DeKalb, Ill., on Friday. ((Charles Rex Arbogast/Associated Press))

Investigators were still piecing together events Thursday at the campus, but do not have any indication of the attacker's motive. University police Chief Donald Grady called the attack "an unfortunate set of circumstances that no one could have predicted."

Sixteen other people were wounded in the shooting, which occurred Thursday afternoon in a lecture hall as students were attending an oceanography class.

During a news conference Friday in DeKalb, Ill., Grady said the shooter kicked open a door at the front of the classroom, entered and quickly began shooting. Police found 48 shell casings and six shotgun shells at the scene.

Grady praised the rapid response of campus police, saying two officers were at the scene less than 30 seconds after it started.

"All this happened before police had a chance to enter the building to stop it," he said.

DeKalb County coroner Dennis Miller also corrected earlier reports that a sixth student had died Friday, saying there had been a mix-up between coroners' offices.

The students killed were identified as Daniel Parmenter, 20, Catalina Garcia, 20, Ryanne Mace, 19, Julianna Gehant, 32, and Gayle Dubowski, 20. All were from Illinois.

Nine of the injured students had been released as of Friday. At least two of the students remaining in hospital trauma care units were scheduled for surgery.

Gunman had recently stopped taking medication

University president John Peters said he spent Thursday night and Friday morning visiting the families of the students who were killed and injured.

"Their response … is heart-rending but I was impressed with their internal strength," he said. "They will get through this with our help and the help and prayers of a lot of people across the country and the world."

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Sorority members of Northern Illinois University participate in a candlelight vigil early Friday. ((Charles Rex Arbogast/Associated Press))

The gunman, who was identified as 27-year-old Stephen Kazmierczak, had recently stopped taking medication.

"He had become somewhat erratic in the past two weeks," Grady said, but declined to say what the medication was for.

Grady said the shooter had three handguns and one shotgun. Two of the weapons — a handgun and the shotgun — had been legally purchased six days earlier, said Grady. Police say they don't know where he got the other two weapons.

The shooter carried the shotgun in a guitar case and wore the others on a belt, which he covered with a coat.

Grady said police still don't have a motive and haven't found any notes from the shooter, a University of Illinois student who was highly regarded by faculty and staff.

"There were no red flags. He was an outstanding student, revered by faculty and staff," he said. "Those who had communication with him felt … he was a fairly normal, unstressed person."

Police are talking with people close to the shooter, said Grady.

The gunman's father, Robert Kazmierczak, briefly came out of his single-storey house in Lakeland, Fla., to talk to reporters.

"Please leave me alone.... This is a very hard time for me," he said as he threw his arms up and wept.

'I could get up and run or I could die here'

Lauren Carr said she was sitting in the third row when she saw the shooter walk through a door on the right-hand side of the stage, pointing a gun straight ahead.

"I personally army-crawled halfway up the aisle," said Carr, a 20-year-old sophomore. "I said I could get up and run or I could die here."

She said a student in front of her was bleeding, "but he just kept running."

"I heard this girl scream, 'Run, he's reloading the gun!' "

About 200 students and other mourners gathered on the campus at about midnight for a candlelight vigil for the victims. Some cried and hugged, while others prayed.

The school will remain closed Friday and all weekend activities on campus have been cancelled.

Peters said counsellors are available in residence halls and other campus buildings.

"All of our personnel have spread out over campus to help students. We've asked them reach out to each other in this difficult time, and they're doing it and I'm proud of them," he said.

Details about upcoming memorials will be made available over the next several days, said Peters.

The university, which has about 25,000 students enrolled, is about 100 kilometres west of Chicago.

Illinois Gov. Rod Blagojevich declared a state of emergency Thursday. The move authorizes money from the state's disaster relief fund to be paid out to local governments that helped out during the shooting.

It's the fourth shooting at an American school in a week. The others were:

  • Feb. 12:  A 14-year-old boy shot a 15-year-old boy in a classroom at E.O. Green Junior High School in Oxnard, Calif. The victim was declared brain dead at hospital.
  • Feb. 11: A 17-year-old is accused of shooting and critically injuring a student during gym class at Mitchell High School in Memphis, Tenn.
  • Feb. 8: A nursing student opened fire at the Louisiana Technical College in Baton Rouge, killing two students before killing herself.
With files from the Associated Press