It doesn’t work this way with bomb precursor material. While there isn’t a government database of the stuff, the FBI and affiliated law enforcement agencies have spent countless hours convincing manufacturers, distributors and retailers to alert the authorities when suspicious or anomalously large purchases of chemical fertilizer or other potential explosives occur. “You would know a lot more about people who buy chemical fertilizer than people who buy firearms,” says Aki Peritz, a former National Counterterrorism Center analyst.



Anyone with $139 plus $12 shipping and handling

can buy on the Internet one of these 100-round

drum magazines for an AR-15 rifle. Unless, that is,

you live in Aurora, Ill.; California; Chicago, Ill.;

Cook County, Ill.; Connecticut; Hawaii; Massachusetts;

New Jersey; New York, South Bend, Ind. or Maryland.

Those alerts apply to people with criminal backgrounds or who are on terrorist watchlists, as well those who don’t. It doesn’t work the same way with firearms. There is no federal database of gun owners or gun purchasers. The Firearms Owners Protection Act of 1986 prohibits the feds from maintaining one. But there are a few exceptions that give law enforcement and intelligence and counterterrorism agents some visibility into private small-arms stockpiles.

First, when someone seeks to buy a gun or rifle from a licensed gun dealer, federally mandated background checks will pick up if the suspected purchaser is on a terrorism watchlist. If so, his or her name will get sent to the FBI’s Terrorist Screening Center. That’s an internal Justice Department practice, not an alert that the gun dealer has anything to do with; indeed, the purchaser won’t know that his name resides in the data banks at the Terrorist Screening Center. However, people on terror watchlists can buy guns.

Another exception, for those that aren’t on terrorist watchlists and don’t have criminal records: Someone seeking to buy two or more of the same kind of rifle will attract the attention of the Bureau of Alcohol, Tobacco and Firearms (ATF). So will someone who tries to buy two or more handguns within five days. The ATF can retain information on those individuals for up to two years. Several counterterrorism sources consulted for this story were unclear as to whether intelligence or counterterrorism operatives could access that ATF data.

Ammunition purchases, however, are functionally unregulated and off-limits to federal law enforcement. The only way law enforcement would know about bulk ammo purchases is if the dealer decides he or she is dealing with a shady customer and alerts the authorities.