A truck entering the CompUSA Plaza in Tyson’s Corner, Virginia, backfired late Monday afternoon. Shoppers on the sidewalk froze. Heads whipped around. A Fairfax County cop eating at a nearby Wendys instinctively reached for his radio mike button.

Another anxious day in the Washington metro area. After eight sniper attacks that left six dead and two wounded – including a 13-year-old Maryland boy fighting for his life – anything that sounded like a gunshot rattled residents of the National Capital Area.

“Yeah, we’re on edge,” said a Virginia State Trooper. “Nobody knows when or where this guy will strike next.”

This guy is a well-trained marksman, a dangerous psychopath who fires from hidden locations, killing victims seemingly at random, yet picking his victims in a cold, calculating manner.

Clint Van Zandt, a former FBI profiler, says he thought he had a handle on the shooter, an alienated young white man who kills for a thrill.

But that was before a single shot from the sniper’s rifle ripped through the abdomen and chest of a 13-year-old boy outside of a Maryland middle school Monday morning. It took doctors some three hours of surgery to remove the young man’s spleen, part of his pancreas, a section of stomach and repair the damage caused by the .223 high powered bullet.

“That shooting changed everything,” Van Zandt says. “It’s one thing to kill a 72-year-old man standing on a street corner. It takes a different personality to shoot a child.”

Cops on the line agree.

“All of our victims have been innocent and defenseless, but now we’re stepping over the line,” Montgomery County Police Chief Charles Moose, tears streaming down his face, said at a press conference Monday, tears streaming down his face. “Shooting a kid – it’s getting to be really, really personal now.”

The shooting spree started last week when the sniper killed six people with six shots on Thursday, victims apparently picked at random – a landscaper mowing a yard, a government employee at a shopping center, a cab driver pumping gas, a woman sitting on a bench, another woman vacuuming out her van and, finally, a 72-year-old man standing on a street corner.

A day later, another single shot from the same high-power rifle struck a woman outside a store in Fredricksburg, Virginia, an hour outside the Washington metro area. Unlike the earlier victims, she lived.

Police knew they were dealing with a cold, calculating killer who always shot from a concealed location, usually 100 to 150 yards away from his victim. The weekend passed with no new shootings and the area relaxed slightly, until another shot rang out Monday morning, sending a 13-year-old boy to the ground, screaming in pain.

“This community is in a state of fear,” says Montgomery County Executive Douglas Duncan said. “We are outraged that someone would do this to our loved ones and our neighbors.”

Moose and Duncan invoked a seldom-used federal law that declared the shootings the work of a serial killer and allowed federal authorities to enter the case. The FBI can enter the case anyway because the killer has crossed state lines.

But every cop entering the case does so with a combination of anger and bewilderment. Anger over a killer who shows no regard for human life, one who willing to kill children; Bewilderment over what kind of person would do such a thing.

“I’ve profiled a lot of killers,” says Van Zandt. “This one defies classification.”

Even if police catch the sniper, we may never know why he did it. Most cops say they don’t think this guy will allow himself to be taken alive. He’ll go down shooting, either taking his own life or forcing cops to kill him.

And no one will mourn his death.

Because whoever this guy is, whatever his motivation, even if his mother never loved him or he never loved this father, this man deserves to die.

When that time comes, I pray to God he suffers.