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[url]http://slate.msn.com/?id=2072107[/url]

Quoted: http://slate.msn.com/?id=2072107

The word "sniper" is often used to describe any shooter who fires a gun from some distance without immediate detection. But the person responsible for the rash of shootings in Maryland, Virginia, and Washington, D.C., appears truly worthy of the designation. This shooter's efficiency, ruthlessness, and deadly accuracy seem to be of the Lee Harvey Oswald (or grassy knoll) variety. Each of the eight victims, including the most recent, a 13-year-old boy, was shot a single time. Six of the victims died almost immediately on the scene.

Does that mean the crimes are unsolvable, left to be debated by conspiracy nuts and turned into a bad Oliver Stone movie? Almost no crime is unsolvable. But time is of the essence. Right now, aside from a single description of a white truck and a white accomplice, the only evidence in police hands seems to be ballistic evidence. Here's some basic police guesswork about what the evidence means.

The weapon used is believed to be a .223-caliber rifle, either a hunting rifle or an assault rifle. A .223-caliber bullet is roughly the same diameter as the traditional .22-caliber bullet that is commonly used to shoot tin cans and small creatures throughout America. The .223, however, has a considerably larger case than the .22. It holds more gunpowder and propels the bullet three times as fast. That's what makes it so deadly. Our sniper can fire one shot and be gone almost before his victim hits the ground.

But the same attributes that make this weapon particularly deadly make the evidence it leaves behind less substantial, and therefore less valuable, than that left by other guns. A nice slow .38-caliber bullet will often stop intact in the victim, where it can be removed by a medical examiner. But rifle bullets, unless they strike a bone within the victim, tend to travel through their targets—sometimes through walls and floors—and stop only when they hit something really hard. That impact tends to reduce them to fragments. Ideally, those fragments will have markings from the rifling of the barrel of the gun that fired the bullet. But don't count on it.

Police have recovered two shell casings. These casings will give them an idea of what kind of gun was used. Different guns and different types of guns leave identifiable dents on shell casings. Firing pins, for example, differ in the shape of the mark they leave on the primer. Imagine a nail that strikes the center of the back of the shell casing when the trigger is pulled. Some are pointier, some are square, and some have little wings. Some strike harder than others. In addition, the marks left on the back of the casing as it is driven against the breech face when it is fired are unique. (The breech face is the wall through which the firing pin protrudes. As the gun is fired, the bullet goes out the barrel and the case travels in the opposite direction, but is stopped by the breech face.) These marks can be compared to other rounds, although this is not nearly as easy or as reliable as examining the fired bullets themselves.

So, what kind of gun is it? Because of its profile and relatively small size, the .223 functions well in automatic and semiautomatic weapons. The pointiness of the bullet tip and the slope of the sides of the case make the cartridges slide by each other in the magazine and into the chamber particularly well. It's the round for which the M-16 and a host of other military rifles are chambered. But these weapons tend to be only moderately accurate. The Maryland sniper is firing only one very accurate shot at his victims.

It's more likely that our sniper is using a hunting rifle. Many people have inherited such rifles, and most states require no permit to buy such guns. It's probably a bolt-action rifle, meaning that the shooter works a handle on the side of the gun that chambers a round and cocks an internal striker. After firing, the shooter must work the handle to eject the round and fire again. Such a gun typically holds five or fewer rounds. It's quite accurate, usually equipped with a scope—and until the action is worked after a shot, it holds the spent shell captive.

There are assault rifles with scopes that are very accurate, but those weapons are highly specialized and expensive. There are also shooters who are such good shots that they can hit a man-size target at several hundred yards using only the iron sites on a regular rifle. But that skill is rare. Given what little we know about the Maryland sniper, the odds are likely that he is using a more mundane hunting rifle. Much easier to get than assault rifles, hunting rifles are generally not subject to gun regulation. This is also bad news for investigators, because it will be much harder to trace the weapon.

So, the evidence that the sniper is using a .223 is not that helpful. Nor is the rest of the limited evidence available. The investigators will use the bullet holes to aim lasers toward the area where it is likely that the sniper was shooting from. They will comb those areas very carefully. In addition, police are performing geographical profiling to try to get an idea of the sniper's center of operations and, presumably, his home. At the very least, this information could help investigators prioritize phone leads.

But what we know about the shooter at this point isn't far removed from common-sense guessing. It is virtually certain that the shooter is male. Women do commit murder, but female snipers are unheard of and female serial killers are tremendously uncommon. At least some access to, knowledge of, and skill with weapons is a given, although an amateur could make these shots with the right rifle out to about 200 yards. Presumably someone capable of repeating such callous and evil crimes is not going to be the most popular and well-adjusted kid in his class. But killers as ambitious and calculating as this one are rare and therefore not easily analyzed or predicted.

The one witness account describing an accomplice seems suspect from the common-sense perspective that sociopathic behavior on this scale is rare. Terrorists aside, to have two people comfortable with random killing is unlikely. The Columbine school shootings were committed by two like-minded perpetrators, but the victims were not chosen completely randomly. On the other hand, a man with a rifle who sets up and waits for a shot in densely populated suburban Maryland will likely attract attention. An accomplice who could watch out for interlopers and assist in flight would make these attacks much easier to commit.

Ultimately, the witness description about a small box truck likely provides the best chance of catching the sniper. In addition to providing him with the ability to shoot from a concealed place, a truck would allow the sniper to carry off any evidence that he might otherwise leave at the scene, such as more spent shells and foreign fibers. Vehicles are easy to trace, and when police do find the truck, it will contain the evidence that the sniper didn't want to leave behind. But given our sniper's skill with a rifle, let's hope that when police do find him, he doesn't see them coming.