OPINION: How can anyone know which students will be dangerous?

Eugene O'Donnell, who teaches at John Jay College of Criminal Justice of the City University of New York, is a former New York City police officer and prosecutor.

A Suffolk teenager who served a year in juvenile detention for planning to stage a Columbine-style attack at Connetquot High School was arrested again not too long ago. The charge? Allegedly hatching a fresh plot to shoot staff and students at the same school.

The allegation that he was planning another rampage, after a year's incarceration, raises questions about how someone with such an incandescent rage should be handled.

Any discussion about school safety should start with the bold restatement of a bedrock truth: America's 119,000 schools are almost universally super-safe havens, where the well-being of students is not an issue. Most high schoolers will go from orientation to graduation with little worry about simple assault, much less mass murder.

But the case of Christopher Franko - who complained that he was berated for living in a trailer park and being overweight, vintage adolescent taunting - unearths issues that go beyond the remote possibility of lethal violence. While it's mostly folly to try to predict assaultive behavior, a 2002 study by the U.S. Secret Service found that of those who did carry out school attacks, most had been verbally or even physically bullied and felt a deep sense of social isolation.

Since that report's release, bullying has reached epidemic proportions, facilitated by social networking - where the victim of a bully can never escape, and scurrilous attacks hang out there in cyberspace. But it's likely that far more of those on the receiving end suffer in silence or harm themselves rather than take up arms against their fellow students.

Another truth is that not all threats are credible, and adults at every level must take responsibility for making commonsense judgments when they arise. Some school administrators invoke a reflexive zero-tolerance approach to threats and student aggression, a policy that is mostly about insulating themselves against blame in the highly unlikely event that something goes wrong. In one Florida school, a student was suspended for bringing a weapon - nail clippers - to class. Another forbids students from bringing a different "weapon" into the school building: "If students are in possession of rubber bands for any reason they will be subject to consequences which may include out of school suspension."

Assessing the likelihood of Franko's conspiracy is very hard to do from outside the investigation itself: Some of the most far-fetched conspiracies can be deadly serious, while unsophisticated plans made by explicit threateners can be just a lot of hot air.

But one chilling aspect of school shootings is that those who actually do act hardly ever make explicit threats in advance. That turns the task of intercepting those with violent designs into a nearly impossible guessing game. Punishing every sullen and oppositional student for trash-talking is a strategy doomed to fail. Conservative commentator John Leo warns against "taking a lot of harmless and minor things ordinary children do and turning them into examples of bullying."

As both a cop and a prosecutor, I was always impressed by the candor of arresting police officers who, even in high-profile cases, would have the guts to say things like, "This is being blown way out of proportion" or "Headquarters is overreacting" or even, "We're arresting the victim - the aggressors got away." Whether dealing with school security or even terrorism, some "plots" are more reminiscent of Walter Mitty than Osama bin Laden.

Protecting schools is vital, but so is protecting the human dignity of the accused. Taking a troubled kid who already feels like the odd person out and throwing him into the justice system is not a permanent solution to anything, and it can even exacerbate the situation. It certainly appears, in this case, that the rage this young man felt did not dissipate as a consequence of his being locked up.

And if a report released late last year is to be believed, New York's juvenile justice system is "harming its children, wasting money and endangering the public."

That report cited the crying need for mental health assistance, which three out of four incarcerated juveniles need, though there is not a single full-time psychiatrist available to these youthful internees. The stigma and damage occasioned by even brief incarceration make it extremely likely that these kids will, one way or the other, forever be wards of ours.

Could it be possible, though, that Franko felt more valued and attended to in lockup than he did in school? He has been quoted as saying the year he spent in a juvenile treatment center "was one of the best experiences of my life."

A 2005 Harvard Medical School study says that mental illness is the country's most prevalent malady, and young people are not immune. Spending any time at all in a youth or adult court or police station will make this obvious. Some of the highest-profile incidents on Long Island in recent months - the Franko case, animal cruelty and hate crimes - have involved some very young people accused of doing some very deranged things.

So in cases where both the threat of violence and the possibility of carrying it out seem real, there cannot be any hesitation in acting swiftly to remove individuals from society - including by means of involuntary civil psychiatric commitment and extremely close probation supervision and monitoring.

As a prosecutor, you wonder a lot about how things could have been done differently to keep cases from coming into criminal court. Could someone have intervened, reached out, engaged the accused, prevented a violent eruption?

But you also know the sad truth that by the time a case makes it to the criminal justice system, there's little more to do than tally the damage all around.