Should people have seen this coming?

PORTLAND, Ore. - There were signs the Virginia Tech shooter could be a threat to others.

Professors and classmates called Seung-Hui Cho's essays and plays disturbing.

Why didn't anyone make a more serious effort to alert authorities?

Experts say it is due in part to human nature and how quickly these kinds of rare crimes can happen.

Just last week, Oregonians experienced a shooting incident at Springwater Trail High School in Gresham, where many students say they knew the suspect, 15-year-old Chad Escobedo, was planning to bring a gun to school. Escobedo is accused of firing two shots into the building. Several students were injured by flying glass.

"He told me yesterday morning he was going to do this, but I thought he was bluffing," one student told KATU News following the shooting.

Criminal profiler Frank Colistro says that kind of reaction after the fact is common.

"A lot of people had little pieces of it, but nobody really knew all of it. So really, the answer is most of the time there is no way to predict these things," Colistro said.

In Virginia, students and teachers stepped forward on Tuesday to reveal shooter Seung-Hui Cho wrote plays depicting horrific violence in his English classes. His work was so disturbing, his instructors referred him to counseling.

Classmates told various newspapers they even suspected he was capable of the worst.

So again: why didn't anyone take those warning signs more seriously and report them earlier?

"Most people are fearful. They don't want to get involved," said Portland-based life coach Karen LaVoie. "If I go to authorities they're going to be grill me about my credibility. How do I know this person? How am I involved in this? Am I really the cause of this problem?"

LaVoie, who teaches independent classes on managing emotions, says there are other factors that keep people silent, including the fear of being wrong and loss of privacy.

Dr. Colistro says the bottom line is that in light of all the violence Americans have seen in recent years, it is still human nature to downplay even the most obvious signs of trouble.

"Most people - at least if they're not into the business of threat assessment - kind of want to believe in the best," Colistro said.

Colistro says signs we can all look for in someone who may pose a danger to others include: noting whether that person is behaving way differently than in the past and paying attention to specific statements that person makes.