Steven Kazmierczak checked into a hotel near Northern Illinois University three days before his deadly shooting spree at the campus, paying cash and signing in under only his first name, the hotel manager said Saturday.

Kazmierczak was last seen at the Travelodge on Tuesday, hotel manager Jay Patel said. Cigarette butts, empty energy drink and cold medicine containers littered the room Friday.

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

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

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Kazmierczak also left a laptop computer, which was seized by investigators, Patel told The Associated Press.

"It's scary," said Patel, adding that he called police when he found the laptop and clothes.

The discoveries added to the puzzles surrounding Kazmierczak, a 27-year-old graduate student some called quiet, dependable and fun-loving. He returned to his alma mater on Valentine's Day and killed five people before turning a gun on himself.

A former employee at a Chicago psychiatric treatment center said Kazmierczak's parents placed him there after high school. She said he used to cut himself, and had resisted taking his medications.

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

Exactly what set Kazmierczak off — and why he picked his former university and that particular lecture hall — remained a mystery.

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On Thursday, Kazmierczak, armed with three handguns and a pump-action shotgun, stepped from behind a screen on the lecture hall's stage and opened fire on a geology class. He killed five students before committing suicide.

University Police Chief Donald Grady said Friday that Kazmierczak had become erratic in the past two weeks after he stopped taking his medication.

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, she said.

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

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

The attack was baffling to many who knew him.

"Steve was the most gentle, quiet guy in the world. ... He had a passion for helping people," said Jim Thomas, an emeritus professor of sociology and criminology at Northern Illinois who taught Kazmierczak, promoted him to a teacher's aide and became his friend.

Kazmierczak once told Thomas about getting a discharge from the Army.

"It was no major deal, a kind of incompatibility discharge — for a state of mind, not for any behavior," Thomas said. "He was concerned that that on his record might be a stigma."

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Kazmierczak enlisted in September 2001, but was discharged in February 2002 for an unspecified reason, Army spokesman Paul Boyce said.

He worked from Sept. 24 to Oct. 9 as a corrections officer at the Rockville Correctional Facility, a medium-security prison in Rockville, Ind. His tenure there ended when "he just didn't show up one day," Indiana prisons spokesman Doug Garrison said.

On Friday, investigators interviewed Kazmierczak's father in Lakeland, Fla., and his former girlfriend in Champaign, the Chicago Tribune reported. Investigators provided no details about what they may have learned.

Authorities were looking into whether Kazmierczak and the woman recently broke up, according to a law enforcement official who spoke to the AP on condition of anonymity because the case is still under investigation.

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, or 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.

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.

Kazmierczak grew up in the Chicago suburb of Elk Grove Village. He was a B student at Elk Grove High School, where school district spokeswoman Venetia Miles said he was active in band and took Japanese before graduating in 1998. He was also in the chess club.

No one answered the door Saturday morning at the Urbana home of Kazmierczak's sister, Susan. But sobs could be heard through the door, where a posted statement said:

"We are both shocked and saddened. In addition to the loss of innocent lives, Steven was a member of our family. We are grieving his loss as well as the loss of life resulting from his actions."

At NIU, six white crosses were placed on a snow-covered hill around the center of campus, which was closed Friday. They included the names of four victims — Daniel Parmenter, Ryanne Mace, Julianna Gehant, Catalina Garcia. The two other crosses were blank, though officials have identified Kazmierczak's final victim as Gayle Dubowski.

By Friday night, dozens of candles flickered in packed snow at makeshift memorials around campus as hundreds of students, mostly wearing the school colors of red and black, packed a memorial service.

"It's kind of overwhelming. It feels strong, it feels like we're all in this together," said Carlee Siggeman, 18, a freshman from Genoa who attended the vigil with friends.