A college gunmen was "off his medication" for an undisclosed condition before he opened fire on an Illinois university campus, the police chief of DeKalb, Ill. said Thursday.

It is not known whether Stephen Kazmierczak, 27, who killed five people and himself at Northern Illinois University on Valentine's Day, was suffering from mental illness or some other condition.

But police did say that, much like the shooter that left 32 people dead at Virginia Tech in April 2007, Kazmierczak was acting erractically in the weeks before the shooting.

Shortly after Seung-Hui Cho's murderous rampage at Virginia Tech, experts told FOXNews.com that there are patterns in school shootings that can help administrators and students understand this type of event.

Dr. Marleen Wong, director of Crisis Counseling and Intervention Services for the Los Angeles Unified School District and director of the Trauma Services Adaptation Center for Schools and Communities in Los Angeles, Calif, said that there have been more than 600 completed school shootings since the late 1980s, with hundreds more foiled by vigilant administrators and police officers.

“A lot of the school shooters have suffered a recent loss, or feel they have suffered a failure, they didn’t have a positive connection with anyone inside their families or outside their families. That was the situation in Canada, at Dawson College, no one knew anything about him,” Wong said, referring to the shooting at Dawson College in September 2006 that left two dead and 19 injured.

Wong said that one of the most important tasks is to recognize threats. “All threats should be taken seriously,” Wong said. “They need to be seen, they need to be referred to mental health services. Homicide and suicide can be two sides of the same coin. Many of the surviving school shooters have saved the last bullet for themselves but were too fearful to carry out the suicide.”

But Wong said it is more difficult to evaluate a potential shooter on a college campus, because of the lack of structure. Attendance is not always taken in class, and it is easy for people to go unnoticed on sprawling campuses.

“The need for mental health services on college campuses is even greater, students have high expectations for themselves. It is a time where they should be sorting out their lives, what their strengths are, what their weaknesses are, but some people feel they are disappointing themselves or their families,” Wong said.

Dr. Spencer Eth, vice chairman of psychiatry at St. Vincent’s Hospital in New York City said there are primarily two groups of people affected by violent events.

The first group are those directly affected, the students who were in the rooms and came directly in contact with the violence. Eth says it is these people who will be at the greatest risk for emotional symptoms.

“Then there are those not directly involved, but they are very frightened as well. You will probably want to include family members with that group,” Eth said. “They have a strong emotional connection with the event but they weren’t in the direct line of fire.”

In addition to those two major groups, Wong also identified those that new the shooter as a group who will be strongly affected. “The other people who knew the young man, sometimes a lot of guilt emerges,” Wong explained.

Eth said that many people will be sad, grief stricken, depressed and anxious after a violent event. Although the grief is overwhelming following the event, Eth says only 10 to 25 percent of the people actually involved directly in the violence should develop psychiatric symptoms, such as post-traumatic stress disorder.

For those that find the memory of this event does not fade, but in fact gets worse, they should seek professional mental counseling.

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