Investigators are gathering DNA evidence they hope will link suspected serial snipers John Allen Muhammad and John Lee Malvo to the Washington, D.C.-area shootings, ABCNEWS has learned.
So far police have been unable to find credible eyewitnesses to any of the shootings that left 10 people dead and three wounded in a three-week span, and it is unclear exactly who pulled the trigger. Because of these obstacles, investigators will have to rely on circumstantial evidence to link the two suspects to the crime scenes.
Sources told ABCNEWS that police have found what appears to be sweat or saliva residue on a package containing a letter demanding $10 million. The package was recovered near the scene of the Oct. 19 shooting of a 37-year-old man outside a Ponderosa restaurant in Ashland, Va.
"Of all the things that a prosecution's team can put before a jury, probably the most compelling thing in America in 2002 is DNA evidence," said former Deputy Attorney General Eric Holder.
The FBI is also planning to conduct DNA tests on what is believed to be human waste found in the woods near one of the shootings and on a raisin box found near another crime scene, sources told ABCNEWS.
According to criminal investigation experts, the federal crime labs at the Bureau of Alcohol, Tobacco and Firearms, FBI, and Secret Service will be using a mix of high-tech tricks and proven analysis techniques to help cement the case against Muhammad and Malvo.
"When you talk about state of the art [forensic] equipment, the labs are in good shape to look at the biologic and document evidence [in this case]," says Lawrence Kobilinsky, a professor of forensic science at John Jay College of Criminal Justice in New York. "The tools are all there."
A key part, obviously, has been the ballistic evidence — the few shell casings and bullet fragments recovered from the multiple crime scenes and victims.
"Ballistic investigation has been around for many years, but the capability has gotten better over the years," says Robert Castelli, a professor of criminal justice at Iona College in New Rochelle, N.Y., and at John Jay. "There are great gains from a technology standpoint. Just in the ability to have greater magnification in comparative microscopes is tremendous."
By examining recovered bullets and casing for similar markings, investigators were able to determine early on that most of the shooting cases were related to the same .223-caliber weapon. More importantly, investigators say they have been able to match that recovered ballistic evidence to the Bushmaster XM-15 rifle that was discovered in the suspects' car upon their capture.
But ballistics evidence is also helping investigators tie Muhammad and Malvo to other shootings as well.
Identifying Other Cases
Two other weapons recovered in the suspects' car have been positively identified with other shootings in Tacoma, Wash., where Muhammad was known to have lived. One of the weapons, a .45-caliber handgun, was used to kill Keenya Cook, the niece of a former employee at Muhammad's auto repair shop.
Outside forensic experts suspect that a computerized ATF database known as the Integrated Ballistic Identification System (IBIS) played a key role in that discovery. IBIS is a collection of digital images bullets and casings recovered by police nationwide to help investigators determine if evidence from one crime can be linked to others.