Forensic Science Isn't Crime-Fighting Cure-All
The bullets, the shell casing and the wounds of the victims. Each piece of evidence seems to offer myriad clues for investigators trying to track the sniper who has terrorized the Washington region for more than a week.
But unlike television shows where crime scene investigators use bullet fragments or a drop of blood to quickly solve a murder, experts say the evidence left by the sniper may not reveal much to help authorities find the killer.
"On a television program, you've got one hour minus commercials to put the whole thing together," says renowned forensic pathologist Cyril Wecht, a past president of the American Academy of Forensic Sciences. "In real life, it's not going to work that way."
On Monday, authorities recovered a tarot card and a shell casing possibly left behind by the sniper. Whether the efforts of scores of federal, state and local investigators can make something of those items remains unclear. Police may also have other evidence that hasn't been disclosed.
But ballistics and forensics experts say little about the shootings themselves -- from the bullets to the wounds -- seems telling.
"Whether this guy is very smart, very lucky or whatever," Wecht says of the sniper, "he's not leaving us anything."
Each shooting victim was struck by a single, .223-caliber bullet, and authorities have matched bullets in seven of 10 shootings. The three other bullets were too shattered to be positively linked. Investigators say they believe the sniper uses a high-powered hunting or military-style rifle and fires from a substantial distance -- perhaps about 150 yards in Monday's shooting of a 13-year-old boy outside a school in Bowie, Md.
Firearms experts were able to link the bullets based on marks imprinted on them from the grooves inside a rifle's barrel. If the marks match, the bullets were fired from the same weapon. In this case, markings on bullets indicate that seven of the shootings were from the same rifle.
But the bullets themselves cannot identify the killer. Experts say they have never heard of a case where police have found the shooter's fingerprint or DNA on a spent bullet. Ballistics experts say no databases list characteristics of the barrels of individual rifles, nor do they know of any registries of those who purchased rifles.
"It doesn't do any good to have the information we have unless we can link it to a particular person," says James Starrs, a George Washington University law professor and forensics teacher.
Bullets can, however, reveal more about a crime than simply the gun that fired them, Starrs says. Analysis of the composition of the metal in a bullet can sometimes identify its manufacturer. In some cases, police have been able to determine which batch of ammunition a specific bullet came from. Police may then be able to track a batch of bullets directly to a local retailer, which might help them identify who bought them, Starrs says.
The shell casing
The metal shell holding the bullet and gunpowder may be even more useful to investigators. A spent casing was recovered in the woods where police investigators say they believe the sniper hid when the 13-year-old boy was shot Monday.
Starrs, a ballistics expert, says the casing can be more valuable in identifying the weapon than a bullet. It will have several distinct markings from the gun and may have the name of the bullet's manufacturer stamped into it.
It also will have a distinct mark from the firing pin. This may enable police to narrow down the types of weapons used. Numerous assault weapons and hunting rifles use .223-caliber shells.
Perhaps more important is what the killer may have left on the casing. The sniper might have touched it and left a fingerprint or a small amount of DNA, says Henry Lee, the former Connecticut State Police crime lab director and a forensic sciences pioneer. Forensics is the use of scientific techniques to solve crime.
Still, unless the sniper has a criminal record with fingerprints or DNA on file, such evidence alone would not lead police to the killer. Like the bullet analysis, it would prove useful primarily in holding or convicting a suspect.
By studying the wounds of the victims, investigators might be able to determine the direction from which the sniper fired. They might also be able to determine a general distance.
But forensic pathologists and firearms experts warn that the wounds themselves tell little.
Without strong eyewitnesses who can describe the position of the victims at the moment they were shot, using entrance and exit wounds to determine the direction of the shooter could prove misleading.
If a victim had turned slightly when the shot was fired, for instance, the trajectory based on entrance and exit wounds might seem to indicate the killer was to one side of the victim when, in reality, the sniper might have fired from directly in front.
"You gotta know where the victim was, obviously, and was the victim sitting, standing, stooping, getting into their car," Wecht says.
The wounds help investigators generally classify the distance between the victim and the sniper, but without much precision in cases of long-distance shooters, ballistics experts say. "In large measure, you won't know precisely how far away it was," says Jon Nordby, a forensic scientist who analyzes crime scenes and trace evidence. "There will be no gunshot residue, no burn powder" on long-distance shootings.
The crime scene
The so-called Death card from the tarot deck was found at the scene of Monday's shooting with the words "Dear Policeman, I am God" written on it.
Like the shell casing also left there, the card might provide a wealth of evidence. The sniper might have left a fingerprint. The handwriting might provide a clue to the shooter's identity. A trace of saliva might contain the person's DNA. The phrase itself might trigger tips from people who suspect someone they know wrote it.
Assuming it was the sniper who left behind the bullet casing and tarot card, police have an idea of the spot from which the shooter fired at the 13-year-old boy.
Pinpointing that location might prove the sort of break investigators need. It means crime scene investigators can employ the latest forensic tools to help solve the case. Did the shooter leave behind hair or fibers from clothing that could identify him or her? How about a footprint? Police might be able to determine where the shooter parked and could search the area for tire tread marks.
If he were working on the case, Lee, who consulted on the O.J. Simpson murder case, says he'd rely on the art of recreating the crime scenes for clues in the case.
So far, it appears that police do not know precisely from where the shots were fired in nine of the 10 shootings. But if they can pinpoint those spots, Lee says, police may be able to find useful evidence: a cigarette butt with the killer's DNA, a tire track from the shooter's car, an image on a surveillance camera."Right now, you are like fishing in the big ocean. You hope for a lucky link to catch him," he says.