"They (lawmakers) feel that the act of amassing those records would in essence go a step toward creating an artificial registration system," Houser said.
What the ATF can do is give trace information to the law enforcement agency that asked for it and in some cases uses the data to help point them in the direction of other crimes.
Houser said the "manually intensive process" can take about five days for a routine trace. In some cases, completing the trace can mean sifting by hand through paperwork that hasn't yet been scanned.
In more urgent situations, including the immediate aftermath of a mass shooting in Connecticut last year, ATF agents run a trace within about 24 hours. Oftentimes, that involves sending agents to the gun dealer that first sold the weapon to quickly find the paperwork listing its original buyer.
Despite having access to millions of records about gun purchases from dealers that have gone out of business, the ATF isn't allowed to create a database of what guns were sold to whom and when.
ATF does keep tabs on how many guns are manufactured and shipped out of the country every year, but only gun makers and dealers know for sure how many are sold. There are also strict limits on what the agency can do with the gun trace information. And that's just the way the gun lobby and Congress want it.
Various laws and spending bills have specifically barred the ATF from creating a national database of guns and gun owners. And due to the efforts of lawmakers, including former Rep. Todd Tiahrt of Kansas, ATF agents who trace the history of a gun can't share that information with anyone but the police agency that asked for it.
As it stands now, local law enforcement doesn't have access to regional data about gun traces. So if the police commissioner in New York City is trying to figure out where the guns are coming into the city from — whether they're going to New Jersey first or upstate New York, for example — that data is not available because of an amendment introduced by Tiahrt, said Mike Bouchard, a former ATF assistant director for Field Operations. ATF can tell police where most crime guns are traced from, by state. But it does not release information on gun shops or purchasers.