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The university gunman who shot and killed five people in a Northern Illinois University lecture hall and then killed himself had recently been acting out of sorts since he stopped taking medicine for an undisclosed condition, police said Friday.

"He had stopped taking medication and become somewhat erratic in the last couple of weeks," Police Chief Don Grady said, declining to name the drug or provide other details.

Carrying a shotgun in a guitar case and at least one handgun registered to him, former sociology graduate student Steven Kazmierczak, 27, kicked through a side door to the 200-capacity Cole Hall, walked in quickly and began firing at students and the teacher, Grady said.

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Police were investigating the motive behind the shootings, which sent 18 people to the hospital. Kazmierczak shot and killed himself on the stage in Cole Hall. There was no known suicide note.

Kazmierczak parked his car near Cole Hall but it was not known how long he had been on campus, Grady said. He had purchased two of the guns just five days earlier.

Illinois Gov. Rod Blagojevich visited campus Friday afternoon to express his condolences.

"Yesterday’s shooting was a tragic, senseless and horrific event," said an emotional Blagojevich. "We saw a terrible act of unthinkable horror."

He urged reporters not to jump to conclusions until all the facts were known, and defended the police response to the tragedy, saying law enforcement was on the scene "within two to three minutes."

In Florida, Polk County sheriff's officials said they were asked to notify the suspect's father — Robert Kazmierczak of Lakeland, Fla. — of his son's death.

The gunman's father, Robert Kazmierczak, briefly came out of his 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. He declined further comment about his son and then went back inside his house, saying he was diabetic.

The Kazmierczaks' Florida home has a sign on the front door that says "Illini fans live here."

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During his time at NIU, Grady said, Kazmierczak "was somewhat revered."

NIU President John Peters also said on Friday ABC's "Good Morning America," "By all accounts that we can tell right now [he] was a very good student that the professors thought well of."

On the school's Web site, Kazmierczak, who no longer was enrolled at Northern Illinois University, still was listed as vice president of the Academic Criminal Justice Association.

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Investigators recovered 48 shell casings and six shotgun shells, Grady said. The gunman paused to reload his shotgun after opening fire on a crowd of terrified students in a geology class.

Kazmierczak had been a graduate student in sociology at Northern Illinois as recently as spring 2007, but was not currently enrolled at the 25,000-student campus, Peters said. He also said the gunman had no record of police contact or an arrest record while attending the university, about 65 miles west of Chicago.

He was currently enrolled as a graduate student at the University of Illinois at Urbana-Champaign, said NIU spokeswoman Melanie Magara.

DeKalb County Coroner Dennis J. Miller identified the five victims who died as Daniel Parmenter, 20, of Westchester, Ill.; Catalina Garcia, 20, of Cicero, Ill.; Ryanne Mace, 19, of Carpentersville, Ill.; Julianna Gehant, 32, of Mendota, Ill.; and Gale Dubowski, 20, of Carol Stream, Ill.

All of the victims sustained gunshot wounds, according to Dr. Roger Maillefer of the Kishwaukee Community Hospital, which treated 18 students who ranged in age from 18 to 27.

As news of the massacre spread, he said, hospital staff spoke with parents as they were stuck in rush-hour traffic trying to get to the hospital, and medical professionals from outside the community volunteered their services to help.

"I literally saw nurses coming off their shifts running back from the parking lot" to assist, Maillefer said.

Witnesses said the 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 Thursday.

Allyse Jerome, 19, a sophomore from Schaumburg, Ill., said the gunman burst through a stage door and pulled out a gun.

"Honestly, at first everyone thought it was a joke," Jerome said. Everyone hit the floor, she said. Then she got up and ran, but tripped. She said she felt like "an open target."

"He could've decided to get me," Jerome said. "I thought for sure he was gonna get me."

John Giovanni, 20, of Des Plaines, Ill., said the gunman calmly fired at the greatest concentration of students.

"He was shooting from the hip. He was just shooting," said Giovanni, who turned and ran so fast that he lost a shoe. "I was running but I was hurtling over people in the fetal position."

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

Two other victims died after being transferred to hospitals in other counties, Miller said. Winnebago County Coroner Sue Fiduccia said a female victim died in her jurisdiction but has not been identified pending notification of family.

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!'"

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More than a hundred students cried and hugged as they gathered outside the Phi Kappa Alpha house early Friday to remember Parmenter, the 20-year-old sophomore, who was one of those killed. Flowers, candles and small notes were left in the snow near Cole Hall.

"I'm not angry," his stepfather, Robert Greer, told the Tribune. "I'm just sad, and I know that right now what I need to do is comfort my wife."

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."

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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.

Of the massacre, he said: "We will get through this together."

FOXNews.com's Heather Scroope and The Associated Press contributed to this report.