This is about mass murder and the U.S. Constitution. The massacre at Virginia Tech may prompt an attitude adjustment toward two parts of this great document – not only the Second Amendment covering the right to bear arms, but the First Amendment protecting freedom of speech.

America is a land of gaping social cracks. The cults of anonymity and open expression make it easy for the homicidal to walk among us unmolested. Cho Seung-Hui, Virginia Tech’s mad killer, was one such individual.

I won’t spend much time here on the gun-control debate. Before the latest carnage, history’s worst school shooting was in Germany, where gun laws are very strict, and before that in Scotland, same story. Had his preferred weapons been banned in the Commonwealth of Virginia, Cho might have obtained them elsewhere. Or he could have made a bomb at home.

But the mainstream case for restricting guns isn’t about banning them all. It’s about who may own what. Virginia could have retained a right to bear arms for hunting or self-defense that did not include letting a mentally ill young man walk out of a Roanoke shop with a Glock 19. And there’s no sane excuse for permitting anyone to buy a weapon with a 15-round ammunition magazine – which was prohibited by the assault-weapons ban that President Bush let expire in 2004.

Cho was a readily identifiable candidate for non-gun ownership, and here’s where our radical defense of free speech causes pain. As the world now knows, Cho wrote wildly violent plays and poetry for a class. His teacher says she became so alarmed by his demeanor and writings that she contacted the campus police, counselors and other supervisors. They evidently did not heed her warnings.

Why not? My guess is that concern for freedom of expression may have trumped worry over strange behavior. School officials might have reasoned: “So what if Cho’s fictional characters want to kill their stepfather and think all girls are whores. That’s the plot of ‘Hamlet.’ We don’t censor here.”

There’s no formula for drawing the line between sadistic imaginings and intent to act out the vision. But it’s much easier to discern real danger when one knows the author. Cho’s poetry teacher clearly had his number – and without being aware that he had been sent to a mental hospital for allegedly threatening female students.

Sociologists note that people bent on mayhem usually emit advance signals of their aims. Charles Whitman, the gunman who in 1966 terrorized the University of Texas at Austin, laid out his plans to the school psychiatrist. Dismissing them as a hostile fantasy, the psychiatrist wrote down that Whitman was “thinking about going up on the tower with a deer rifle and start shooting people.”

The 1999 tragedy at Columbine High led to the federal COPS in Schools program, which identifies disturbed students planning mayhem. Specially trained officers hang out with the students, giving them a means to privately relate suspicions of coming violence. The “stop cops” have been credited with cutting off many plots. The Bush administration and Congress last year chopped funding for the program.

The alternative is dealing with an attack in progress. The slaughter at UT did help inspire the creation of SWAT teams. And the Virginia Tech horror now has campus security forces making contingency plans for similar assaults.

It’s probably more effective, though, to find and remove these potential killers – and try to deny them the most lethal hardware. That means we must detain them for their words and deny them guns.

As we see time and again, the right to bear arms and be crazy is a deadly combination.