Microscopic clues on a bullet fragment or a shell casing recovered from a victim or at a crime scene provide crucial information for investigators trying to catch a clandestine shooter.
Ballistics analysis by the Treasury Department's Bureau of Alcohol, Tobacco and Firearms is a key part of the investigation into the sniper attacks that have terrorized the Washington area. On Tuesday, Attorney General John Ashcroft underscored the federal role, pledging that the Justice Department would also do "everything we can to solve this."
Though ATF officials have not discussed the sniper case specifically, firearms examiners working out of an ATF lab in Rockville, Md., are on the front lines of unraveling clues that are left behind -- microscopic scratches and dents -- on the bullets, their fragments or cartridge casings. This information can help investigators determine what type and make of firearm fired the bullet.
"Every firearm has individual characteristics that are as unique to it as fingerprints are to human beings," says an ATF report on bullet tracing.
Grooves inside the barrel of a gun help a bullet travel with precision. When a bullet is fired, these grooves and other unique characteristics are imprinted on the bullet as it travels through the barrel. When a bullet or bullet fragment is recovered from a crime, it is examined to see if a pattern of grooves and "lands" -- which refers to the distance between the grooves ---- can pinpoint the type of firearm that was used. Examiners also weigh the bullet or bullet fragments to try to identify the caliber and type of firearm.
Bullet casings also can have distinctive markings created by the gun's firing pin, ejector and the breech mechanism ---- the place where the bullet sits in the barrel of the gun. Sometimes a fragment can be too small, or shattered, making any markings all but impossible to divine, ATF officials said.
Digital images of the bullet or bullet casing are stored in ATF's National Integrated Ballistic Information Network, a computer database that contains images of casings or bullets from crime scenes, as well as casings or bullets from test firings of weapons used in crimes.
The database allows investigators to link crimes by comparing bullets and cartridge casings found at one crime scene with those found at another. When a likely match is found, firearms examiners "repeat the comparison with the actual evidence to confirm the match," according to an ATF report on the system.
In the Washington-area sniper attacks, police acknowledge having few clues or eyewitness accounts to solve one of the most frightening serial killings in the region's memory. A task force including local and state police, the FBI and the Secret Service is pursuing the sniper.
On Tuesday, Ashcroft telephoned Montgomery County, Md., Police Chief Charles Moose, thanking Moose for a letter requesting Justice Department assistance, saying, "We want to make sure we are doing everything we can to solve this."
Since last Wednesday, the sniper has shot eight people, killing six. Police have discerned no pattern among the victims. One died on a Washington street, the others within five miles of each other in Maryland's Montgomery County. In the latest attack, a 13-year old boy was shot Monday as his aunt dropped him off at his school in Maryland's Prince George's County.
Ballistics tests found the bullet that struck the teen was identical to those that killed some of the others and wounded a woman in Virginia, said Joe Riehl, an ATF agent. All victims were hit by a single bullet fired from a distance. Police have spoken of a single sniper, but have not ruled out the possibility that more than one person is involved.