WASHINGTON -- The question that cries out for answers in the Virginia Tech massacre is, why didn't anyone pull together all of the psychopathic clues about Cho Seung-Hui before he went on his killing rampage?

Those clues have been tumbling out in the aftermath of the worst mass murder in American history by a single gunman. They inexorably lead to one painful inquiry: How could the university system allow Cho to stay on campus and attend classes when so many people knew he was a deeply disturbed, mentally ill young man who frightened students and teachers alike?

An English teacher was deeply troubled by his bizarre writings about death and killings, and his sullen, uncommunicative behavior in class. That behavior reached a point where she came to class to find most of her students absent because they were afraid of Cho, who talked to no one and took pictures of them. His classmates sensed something was very wrong with him.

Another teacher chose to tutor Cho separately, urging him to seek out counseling, which he refused to do. She notified her superiors, but it seems they felt powerless to act, and we now know that no one looked into the senior English major's troubled past until it was too late.

Then more troubling reports of his past came out. He had approached and messaged two women in separate incidents, which they reported to the university security authorities. No charges were filed against him, but he underwent an examination at a mental-health facility following a temporary detention order signed by a judge.

The judge checked off the box that said Cho may be suicidal, but did not check off the box suggesting he could be danger to others. The mental-health-examination documents record that he was "depressed" but did not represent a threat to others or require involuntary treatment.

But the insane rantings in his computer and the menacing, gun-wielding videos and hate writings he sent to NBC News fully revealed a deranged man who foretold of his plans to kill as many people as he could before taking his own life.

"You forced me into a corner and gave me only one option. The decision was yours. Now you have blood on your hands that will never wash off," he said on the video he had recorded, probably long before last week's deadly events unfolded.

These and other signs were there for anyone who took the trouble to examine this man's psychotic past and "connect the dots," the famous line about the trail of clues that led up to the 9/11 attacks on America.

"Every day, every hour, more people came forward who knew that something was deeply wrong with Cho Seung-Hui. Teachers, roommates, classmates from college, high school, middle school -- people knew," reporter Marc Fisher wrote in The Washington Post.

"And people acted. Not all of them, and not all in loud and useful ways, but some who were disturbed by Cho's actions and words did what we would want them to do. They told somebody. And still, here we are. Why?" Fisher asked.

But what could have been done? Well, how is it that when he refused mental counseling, he was allowed to remain in class? Or, for that matter, remain at the university?

University officials have a responsibility to help individual students who are distressed or troubled, but they have a larger responsibility to provide a safe, secure environment for their student body and faculty. Clearly, they failed in that solemn responsibility.

If the events leading up to the slaughter at Virginia Tech sound familiar, that's because the very same thing happened at Columbine High School in Littleton, Colo., eight years ago. Two teenage killers, Dylan Klebold and Eric Harris, went on a rampage that they, too, had meticulously planned out. And, like Cho, they had left a computer and paper trail of their deadly intentions.

They "wrote school papers about their plan. They put up a Web site about it.

Harris even wrote in court documents that he was homicidal and suicidal," Fisher recounted. "People knew. Still, Columbine happened."

A special commission is being appointed by the governor to examine how the university handled all of this, what was known about Cho's past and what could have been done that might have avoided last week's massacre.

There are some basic lessons to be learned here. Disturbed students need treatment and involuntary hospitalization, if need be, not just student/teacher counseling. Teachers and college officials need to more closely assess a troubled student's past and understand the signs of depression, bipolar disorders, paranoia and homicidal rage. Excessive writings about killing people need to be taken seriously.

Teachers, counselors and students need to be encouraged to talk to school authorities and health professionals about disturbing behavior, and there must be a system in place to examine and respond to such reports.

The lesson of Columbine and Virginia Tech is that many people knew but no one acted preemptively to prevent this tragedy from occurring.