A former student dressed in black walked onto the stage of a lecture hall at Northern Illinois University and opened fire on a packed science class Thursday, killing six students, wounding 15 and setting off a panicked stampede before committing suicide, FOX News has confirmed.

"I kept thinking, 'Oh, God, he's going to shoot me. Oh, God, I'm dead. I'm dead. I'm dead,"' said Desiree Smith, a senior journalism major who dropped to the floor near the back of the auditorium.

The gunman was identified as Steven Kazmierczak, a university official told The Associated Press on condition of anonymity because the name had not been released by police.

Polk County, Fla., sheriff's officials said they were asked to speak with "the father of the shooting suspect," Robert Kazmierczak, of Lakeland, Fla.

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Police said they had no motive for the rapid-fire assault by Kazmierczak, who fired indiscriminately into the crowd with a shotgun and two handguns as students dove to the floor and ran toward the exits.

"People were crawling on each other, trampling each other," she said. "As I got near the door, I got up and I started running."

On Friday President Bush offered his condolences in a phone call with NIU President John Peters.

"This morning I spoke to the president of Northern Illinois University. I told the president that a lot of folks today would be praying for the families of the victims and for the Northern Illinois University community," Bush said. "Obviously a tragic situation on that campus, and I ask our fellow citizens to offer their blessings — blessings of comfort and blessings of strength."

DeKalb County Coroner Dennis J. Miller released the identities of four of the victims: Daniel Parmenter, 20, of Westchester; Catalina Garcia, 20, of Cicero; Ryanne Mace, 19, of Carpentersville; and Julianna Gehant, 32, of Meridan.

Peters said four people died at the scene, including three students and the gunman while the other three died at a hospital. The teacher, a graduate student, was wounded but expected to recover.

Peters said the gunman was a former graduate student in sociology at NIU, but was not currently enrolled at the 25,000-student campus about 65 miles west of Chicago.

"It appears he may have been a student somewhere else," University Police Chief Donald Grady said.

Witnesses said the thin gunman, dressed in black and wearing a stocking cap, emerged from behind a screen on the stage of 200-seat Cole Hall and opened fire just as the class was about to end around 3 p.m.

Officials said 162 students were registered for the class but it was unknown how many were there on Thursday.

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."'

Student Jerry Santoni was in a back row when he saw the gunman enter a service door to the stage.

"I saw him shoot one round at the teacher," he said. "After that, I proceeded to get down as fast as I could."

Santoni dived down, hitting his head the seat in front of him, leaving a knot about half the size of a pingpong ball on his forehead.

Seventeen victims were brought to nearby Kishwaukee Community Hospital, where one died, according to spokeswoman Theresa Komitas. One male was transferred in critical condition and died at OSF St. Anthony Medical Center in Rockford, an official said.

Dan Parmenter, a 20-year-old sophomore from Elmhurst, Ill., was one of those killed, his stepfather, Robert Greer, told the Chicago Tribune.

"I'm not angry," Greer said. "I'm just sad, and I know that right now what I need to do is comfort my wife."

Minutes after the shooting erupted, students phoned each other and sent text messages even before school officials could warn them, many said. The school Web site announced a possible gunman on campus within 20 minutes of the shots and locked down the campus, part of a new security plan created after a student at Virginia Tech killed 32 people last year.

"This is a tragedy, but from all indications we did everything we could when we found out," Peters said.

Michael Gentile was meeting with two of his students directly beneath the lecture hall when the shootings happened. He could hear the chaos a few feet above his head.

"The shotgun blast must have been so loud," said Gentile, a 27-year-old media studies instructor. "It sounded like something was dropping down the stairs. ... We had no idea what this was."

Then, shorter, sharper noises he recognized as handgun shots.

"There was a pretty quick succession ... just pow, pow, pow," said Gentile, who didn't leave his office for about 90 minutes. He used a surveillance camera just outside his office to confirm that the people knocking on his door were police.

George Gaynor, a senior geography student who was in Cole Hall when the shooting happened, told the student newspaper the Northern Star that the shooter was "a skinny white guy with a stocking cap on."

He described the scene immediately following the incident as terrifying and chaotic.

"Some girl got hit in the eye. A guy got hit in the leg," Gaynor said outside just minutes after the shooting. "It was like five minutes before class ended, too."

Student Edward Robinson told WLS that the gunman appeared to target students in one part of the lecture hall.

"It was almost like he knew who he wanted to shoot," Robinson said. "He knew who and where he wanted to be firing at."

The federal Bureau of Alcohol, Tobacco and Firearms sent 15 agents to the scene, according to spokesman Thomas Ahern. He said information about the weapons involved would be sent to the ATF's national database in Washington and given urgent priority. The FBI also was assisting.

All classes were canceled Thursday night and the campus was closed on Friday. Students were urged to call their parents "as soon as possible" and were offered counseling at any residence hall, according to the school Web site.

The school was closed for one day during final exam week in December after campus police found threats, including racial slurs and references to shootings earlier in the year at Virginia Tech, scrawled on a bathroom wall in a dormitory.

Police determined after an investigation that there was no imminent threat and the campus was reopened. Peters said he knew of no connection between that incident and Thursday's attack.

The shooting was the fourth at a U.S. school within a week.

On Feb. 8, a woman shot two fellow students to death before committing suicide at Louisiana Technical College in Baton Rouge. In Memphis, Tenn., a 17-year-old is accused of shooting and critically wounding a fellow student Monday during a high school gym class, and the 15-year-old victim of a shooting at an Oxnard, Calif., junior high school has been declared brain dead.

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The Associated Press contributed to this report.