Every time somebody pulls the trigger on a gun, it leaves distinctive marks on the bullet or cartridge case. Police have long used those tell-tale marks to help them link a gun to a crime, and bullet-matching is a regular feature of police dramas like CSI.
In recent years, some lawmakers and gun control groups have pushed for a national database that would record the ballistics signature of every gun sold in the United States. But a new report from a prestigious scientific panel says it's probably not a good idea.
The series of deadly sniper shootings in the Washington, D.C., area in October 2002 inspired some lawmakers to start thinking about a national database.
By comparing bullets taken from the victims, investigators knew that the shootings were linked. But to what gun? Whose gun? Police couldn't tell. The federal government does have a database of markings on bullets that police can search, but it includes only guns that have been already used in a crime.
That led some lawmakers to wonder whether the unique markings left by all guns should be recorded — whether the guns should be fired and their ballistic signatures noted before they were sold. That way, if the guns were ever used in crimes, investigators could trace them.
But it wasn't clear if the technology was ready. So the Department of Justice took the problem to the National Research Council, which gives the government independent advice on science issues. A panel spent four years looking at the idea.
The panel's verdict? "At this time, it really is not feasible," says John Rolph, who chaired the panel. Rolph is a statistician from the University of Southern California.
"We sell between 1 and 2 million handguns in the United States each year. So if you were to enter every single gun, you'd be entering 1 to 2 million every year," he explains.
Rolph says today's technology for comparing images would have a hard time sorting through so many. It would spit out lots of possible matches.
"It never tells you — like on CSI — 'this is a match.' It tells you, 'here's some potential candidates,'" he says.
Getting too many candidates would be a big problem — because to know if a match is real, a forensics expert would have to pull the evidence for closer examination.
"It's OK to have them look at maybe 10 or 20. Do you want them to look at several hundred? ... It would be really very difficult to use in a practical way," he says.
So far only two states, New York and Maryland, have set up systems to gather ballistics images from all guns sold or manufactured in those states. Both programs have come under fire from critics who say they cost a lot of money and haven't really helped the police.
"We've watched what's happened in Maryland and New York, and they have sort of test systems. And we've known that while, you know, I think the design was done in good faith, there's some problems in execution," says Joshua Horowitz, executive director of the Educational Fund to Stop Gun Violence.
He says the experience in those states is one reason why gun control advocates are interested in a newer kind of bullet-tracing technology, called "microstamping." The idea is to design guns so that every time they fire, they stamp a unique identifying code onto a bullet or cartridge case.
"So we've really changed our emphasis to this because it gets around many of these problems that we sort of identified three or four years ago," Horowitz says.
California has already passed a limited microstamping law that takes effect in 2010. It will require new semiautomatic handguns to microstamp each cartridge case of a fired round of ammunition. Horowitz says eight other states are considering similar legislation. But critics of microstamping, like the National Rifle Association, say criminals will be able to easily tamper with the marks.
In its report, the National Research Council panel said microstamping looked like a promising technology. But it also said more in-depth studies are needed.