In the course of four months, in a span of roughly a dozen miles, two homicidal lunatics have shot and killed six people.

George Sodini killed three women and wounded nine others Tuesday in Collier. Richard Poplawski is accused of killing three Pittsburgh police officers exactly four months earlier. The men have much in common. Both are --or were -- Internet-savvy, hate-filled guys who bought a small pile of guns and fulfilled sick fantasies that will forever torture innocent survivors.

Both also live -- or lived -- in a country that will have great difficulty keeping these incidents from happening again. And again.

The guns these men wielded were bought legally. But under the old federal assault weapons law that expired in 2004, both the 30-round ammunition clips that Mr. Sodini used before killing himself, and the AK-47 that Mr. Poplawski used, would have been illegal.

If you don't know why such a seemingly sensible ban expired, you've never listened to talk radio.

We do have in this country a constitutional right to bear arms. The Founding Fathers placed it high in the Bill of Rights, just after the First Amendment freedoms of speech and religion. That's inarguable. What has been argued off and on for more than two centuries is precisely what these men from the age of muskets meant when they penned what might be the most haphazardly constructed English sentence of all time:

"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

The Pennsylvania Constitution is more straightforward: "The right of the citizens to bear arms in defense of themselves and the State shall not be questioned."

Every right is subject to some limitations. The right to free speech doesn't include the right to slander, libel, etc. Exactly how the individual right to bear arms jibes with that "well regulated militia'' may not be clear, but even a Second Amendment stalwart such as Supreme Court Justice Antonin Scalia says "laws imposing conditions and qualifications on the commercial sale of arms'' are permissible. Justice Scalia said as much in his opinion overturning the home handgun ban in Washington, D.C., last year.

That left the door open for restricting gun purchases to one a month and banning assault weapons. The former, but especially the latter, might have made a difference in Pittsburgh this year.

What do our homegrown killers have in common?

1) Each man acquired not just a gun, but a small arsenal. Mr. Sodini carried four guns into the LA Fitness Center. Two 9mm pistols with 30-round clips, two extra 30-round clips and a .45-caliber pistol were in his gym bag. He also had a .32 semiautomatic pistol in his pocket. Police estimated he carried 150 rounds -- to an aerobics class. Detectives also found four rifles and shotguns in his Scott home, where he lived alone.

Poplawski, who knew his mother had called 911, set up his ambush of police in Stanton Heights with an AK-47, a shotgun and a revolver, while wearing a bulletproof vest.

2) While it's true that the shooter, not the weapon, is to blame, mass murderers seem to gain what passes in their world for courage when they get heavy with firepower. Mr. Poplawski praised his AK-47 in a Web posting last December, and was charged with using it to slay three men in April.

Mr. Sodini didn't go on about weaponry in the diary he posted on the Internet, but he mentioned that he needed booze, after more than 20 years off the stuff, to "embolden me.'' It's easy to believe this maladjusted man wouldn't have summoned the nerve, and he'd have difficulty killing and wounding so many in a minute's time, without the 30-round clips.

Rep. Joe Sestak, the retired U.S. Navy admiral who is taking on Sen. Arlen Specter for the Democratic nomination for the U.S. Senate in 2010, is co-sponsoring a reinstatement of the assault weapons ban. Mr. Sestak had 31 years in the military and supports "the legitimate right to bear arms,'' but the killings in and around Pittsburgh "are heartbreaking reminders that we must immediately address the loss of the commonsense ban earlier in this decade.''

Mr. Specter voted against extending the assault weapons ban in 2004. Asked for comment on Friday, he was noncommittal but leaned toward the same position: "Since studies commissioned by the Department of Justice and the Centers for Disease Control have questioned the effectiveness of a ban on assault weapons in reducing crimes, there should be a hearing to determine the facts on what effect the ban had, contrasted with what happened without the ban ...

"In any event, it does not appear that a ban would have prevented the tragic shooting at the health club in Pittsburgh. My experience as district attorney shows the best way to deal with gun violence is long jail sentences."

Peg Luksik, seeking the Republican nomination, says she is against banning assault weapons, saying citizens need them for self-defense.

Her opponent, Pat Toomey, said, "Whenever there's an outrageous criminal use of guns, liberals like Joe Sestak always try to penalize law-abiding gun owners rather than holding criminals responsible. Sestak is wrong. We should punish criminals and protect gun ownership rights.''

Mr. Poplawski and Mr. Sodini were obeying the law right up to the moments they killed six people between them.