The evidence is conclusive.
But they don't know precisely how to track his gun, because, as CBS New Correspondent Wyatt Andrews reports, gun ownership records are not computerized.
At his Maryland gun range, Carl Roy explains how gun ownership records are physically kept by gun shops and still must be checked by hand. Searches for the sniper's weapon then, are being conducted gun shop-by-gun shop, beginning in handwritten log books: a laborious, time-consuming task.
Some in Congress believe gun crimes can easily be connected to owners with what's called a ballistic fingerprint database, where every gun is test-fired and the marking from its bullets digitally recorded.
"How crazy is this, today in the D.C. metropolitan area, the FBI and the local police are searching through 8,000 white vans to try to find this shooter or shooters," says congressman Rob Andrews, D-N.J. "Why search 8,000 vans when you can search for one gun, if this technology were used."
For the last two years, Maryland has had a state law where the brass ejected from every weapon must be submitted to the state police.
The problem with brass fingerprints, Roy says, is they're not always accurate. The markings change. In fact, the White House began this week played down the accuracy of ballistic fingerprints, but quickly backtracked when President George W. Bush decided it's worth a look.
"The President wants this issue explored," says Whitehouse spokesman Ari Fleischer.
So far the NRA has blocked the fingerprint idea as a concept too close to national registration. But add this to the list of ways the sniper has had an impact. He is fast becoming a poster child for a database of the nations guns.