DEKALB, Ill. - Steven Kazmierczak had the look of a boyish graduate student — except for the disturbing tattoos that covered his arms. Professors and students knew him as a bright, helpful scholar, but his past included a stint in a mental health center.

 Many saw him as happy and stable, but he had developed a recent interest in guns and was involved in a troubled — possibly abusive — on-again, off-again relationship.

What people initially told police about the Northern Illinois University shooter didn't add up, and now investigators are searching for answers to what triggered Thursday's bloody attack, in which five students were killed and several more injured before Kazmierczak committed suicide.

While searching for a motive, authorities questioned family and friends and tried to determine whether he had recently broken up with his longtime girlfriend.

One person who knew the couple, who spoke to The Associated Press on the condition of anonymity, said the couple's relationship was on-again, off-again and "really rocky." Kazmierczak was controlling, she said.

"He was abusive, had a temper," she said. "He didn't actually hit her; he would push her around."

The 27-year-old Kazmierczak also had a history of mental illness and had become erratic in the past two weeks after he stopped taking his medication, said university Police Chief Donald Grady.

A former employee at a Chicago psychiatric treatment center said Kazmierczak had been placed there after high school by his parents. He used to cut himself and had resisted taking his medications, she said.

Kazmierczak spent more than a year at the Thresholds-Mary Hill House in the late 1990s, former house manager Louise Gbadamashi told The Associated Press. His parents placed him there after high school because he had become "unruly" at home, she said.

Gbadamashi couldn't remember any instances of him being violent, she said.

"He never wanted to identify with being mentally ill," she said. "That was part of the problem."

Jason Dunavan, a tattoo artist in Champaign, said he spent hours as recently as last month creating tattoos for Kazmierczak. His work included an image of the macabre doll from the horror movie "Saw" riding a tricycle through a pool of blood with images of several bleeding cuts in the background.

Dunavan said he was so proud of the tattoo that he enlarged a photo of it and placed it on a wall in his shop — a move he is now rethinking.

"I don't know if I still want that picture on my wall," said Dunavan, who also described Kazmierczak as timid and apologetic.

"He was really, really mousy."

On Friday, police went through belongings Kazmierczak left at a DeKalb motel in search of clues.

Kazmierczak paid cash for his room at the Travelodge three days before the shootings, signing his name only as "Steven" on a slip of paper, according to the hotel manager. Items later found in his room included empty cartons of cigarettes and discarded containers of energy drinks and cold medicine. The refrigerator was stocked with more energy drinks.

Authorities found a duffel bag, with the zippers glued shut, that Kazmierczak had left in the room, said Lt. Gary Spangler of the DeKalb Police Department. A bomb squad safely opened the bag Friday, Spangler said.

He would not comment on what was found in the bag. The Chicago Tribune, citing law enforcement sources, reported that investigators found ammunition inside.

Kazmierczak also left behind a laptop computer, which was seized by investigators, said Jay Patel, manager at the Travelodge.

The discoveries added to the puzzles surrounding Kazmierczak, a graduate student who had once studied at Northern Illinois University but transferred to the University of Illinois at Urbana-Champaign.

He also had a short-lived stint as a prison guard that ended abruptly when he didn't show up for work. He was in the Army for about six months in 2001-02, but he told a friend he'd gotten a psychological discharge.

Those who knew him were baffled by the attacks, in which Kazmierczak stepped from behind a screen on the lecture hall's stage and opened fire on a geology class.

Jim Thomas, an emeritus professor of sociology and criminology at NIU who taught Kazmierczak, insisted there was no indication of trouble between Kazmierczak and his girlfriend.

"I do know they loved each other very much," Thomas said. "He felt extremely close to her. ... To my knowledge, I saw no indication of abuse."

Kazmierczak's godfather, Richard Grafer, said Saturday that his godson was in good spirits when they spoke Tuesday about playing chess sometime soon.

Kazmierczak told his godfather he would call him again Saturday. "He seemed fine, great. We were laughing and talking and telling jokes," said Grafer, who added that he knew nothing about Kazmierczak being on or off medication.

Kristen Myers, an associate professor of sociology who knew Kazmierczak, also said he didn't fit the image of a loner or outcast.

"Profiling would not have worked with Steve. People would let him into their home," she said. "People feel so bad that we didn't know he was suffering like this."

On Feb. 9, Kazmierczak walked into a Champaign gun store and picked up two guns — a Remington shotgun and a Glock 9mm handgun. He bought the two other handguns at the same shop — a Hi-Point .380 on Dec. 30 and a Sig Sauer on Aug. 6.

All four guns were bought legally from a federally licensed firearms dealer, said Thomas Ahern, a spokesman for the federal Bureau of Alcohol, Tobacco, Firearms and Explosives. At least one criminal background check was performed — Kazmierczak had no criminal record.

Kazmierczak had a state police-issued FOID, a firearms owners identification card, which is required in Illinois to own a gun, authorities said. Such cards are rarely issued to those with recent mental health problems. And since Kazmierczak's stay in the mental health center was more than five years ago, it didn't raise red flags.

NIU President John Peters said Kazmierczak compiled "a very good academic record, no record of trouble" at the 25,000-student campus in DeKalb. He won at least two awards and served as an officer in two student groups dedicated to promoting understanding of the criminal justice system.

Seven people remained hospitalized Saturday after the attack, with three in serious condition, one of them upgraded from critical. The other four are in fair condition.

Officials at NIU said classes will resume on Feb. 25, though Cole Hall — where the shootings happened — will remained closed until the end of the semester.

Peters promised a strong police presence and ample counseling for students and instructors.

"We need to take care of ourselves and each other, reaching out to those of us who are struggling," Peters said in a statement.

"An act of violence does not define us."

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Contributing to this report were Associated Press writers Karen Hawkins, Nguyen Huy Vu, Don Babwin, Deanna Bellandi, Dave Carpenter, Tamara Starks, Carla K. Johnson, Michael Tarm and Mike Robinson in Illinois; Anthony McCartney in Lakeland, Fla.; Matt Apuzzo and Lolita Baldor in Washington; AP National Writer Martha Irvine; and the AP News Research Center in New York.