The gunman who shot dead five people at a university in Dekalb, Illinois has been identified as an "outstanding" graduate student with no history of trouble but signs of erratic behaviour in the last two weeks.
Officials drew a mixed picture of Stephen Kazmierczak, 27, who opened fire in a lecture hall at Northern Illinois University Thursday, killing five students and wounding 16 others before turning his gun on himself.
"He was an outstanding student," university police chief Donald Grady told a news conference on Friday. "He was someone that was revered by the faculty and staff and students alike."
"We had no indication at all that this would be the type of person to engage in this type of activity."
Officials said Kazmierczak was enrolled at Northern Illinois last year but was a graduate student in social work at another area school, the University of Illinois at Urbana-Champaign, at the time of the shooting.
"He was a fairly normal, unstressed person," Grady said. But he added that Kazmierczak's family reported the gunman had been on some unnamed medication and stopped taking it.
"He had been somewhat erratic in the last two weeks," the police chief said, without elaborating. He said Kazmierczak left no note and there was no clue as to the motive behind the mass shooting.
There was no indication that Kazmierczak knew anyone in the geology class with 162 registered students, and Grady dismissed rumors that the Valentine's Day carnage was the result of a jilted love affair.
A bright, award-winning student who had co-authored paper on self-injury and the role of religion in prisons, Kazmierczak did not fit the usual profile of a mass murderer.
"I knew him as a warm, sensitive, very bright student," professor Kristen Myers said in an email.
"I never would believe that he could do this. I know that when these horrible things happen, everyone searches for roots to explain it. Here, I'm afraid I don't have any."
Criminology professor Jim Thomas, who mentored Kazmierczak for years, was shocked that such a "gentle, even guy" could have snapped to such an extent.
While Kazmierczak had told Thomas that he'd been discharged from the military for psychological reasons, "he seemed as normal as you or I."
US President George W Bush regretted the "tragic" incident.
"Obviously, a tragic situation on that campus, and I asked our fellow citizens to offer their blessings," Bush said.
Officials and witnesses said that Kazmierczak, armed with a shotgun and three handguns, calmly stepped out from behind a curtain at the front of the auditorium just minutes before the end of class.
Screams filled the hall as he sprayed bullets into the auditorium filled with dozens of students at the campus in DeKalb, a small town west of Chicago.
"He just fired directly into the audience," said John Giovanni, a student in the class. "He didn't say a word. It didn't look like he was aiming directly at someone. I think he was trying to hit as many people as he could."
Screaming students ducked for cover, some crawling on their bellies, others cowering behind seats while others made for the doors.
Even though it lasted less than two minutes, Kazmierczak found time to reload his shotgun and police found 48 bullet casings and six shotgun shells scattered across the auditorium.
The massacre was the fifth school shooting in a week, following episodes in Ohio, Louisiana, Tennessee and California that left a total of five dead.
And it came 10 months after 32 students and faculty were shot down by a mentally disturbed student at Virginia Tech University in the deadliest massacre ever at a US school.
Northern Illinois University was placed on a security alert in December after police found threats on a bathroom wall laced with racial slurs, references to the Virginia Tech shooting and a warning that "things will change most hastily" in the final days of the semester.
But university president John Peters said he did not think Thursday's shooting was related to the threats and said that while security has been heightened, there was not much more officials could have done.
US campus shooter 'was bright but erratic’