A former graduate student dressed in black trench coat and wearing a ski mask opened fire with a shotgun and two handguns from the stage of a lecture hall at Northern Illinois University yesterday, killing five students and wounding 16 before committing suicide, authorities said.

The gunman was identified as 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 quoted by the Associated Press.

The man, described by one student as a “skinny white guy,” emerged from behind a curtain and fired 20 or 30 shots.

“This guy came in from behind where the professor was speaking and began shooting. He shot, emptied out the gun, and nonchalantly began reloading,” Paul Sundstrom, a student said in an interview posted on MSNBC.com. He also said that about 150 to 200 students were in the lecture room at the time.

Then the gunman shot himself on the stage after the brief rampage that sent terrified student screaming and running for the doors about 3 p.m.

“I ducked behind the seats and ran out the door. As I was running, I just kept waiting for something to hit me in the back. I didn’t know where to run, tried to decide where it’s safe to be, and there isn’t anywhere safe,” student Zach Seward told local Daily Chronicle newspaper.

University president John Peters said four students died at the scene, including the gunman, and the other two died at a hospital. The teacher, a graduate student, was injured but was expected to recover.

Sixteen other wounded students were taken to nearby Kishwaukee Community Hospital to receive appropriate care.

“We have no motive. I have no way of knowing what his motive was,” Grady said.

The shooting comes just two months after 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. The school was closed for one day, but reopened after an investigation concluding there was no imminent threat.

Also, the incident was the fourth at a U.S. school in just one week. On Feb. 8, a woman gunned down two students at Louisiana Technical College in Baton Rouge. On Monday, a 17-year-old gunman opened fire at a Memphis high school, critically injuring a fellow student during gym class. A day later, a 14-year-old junior high school student shot a classmate in the head in Oxnard, Calif.