Cue Lee Greenwood.

Investigators now believe that the Tsarnaev brothers had a single gun between them, a Ruger 9mm semi-automatic handgun that they are suspected of using to kill an MIT police officer, Sean Collier, and to engage in a fearsome firefight with police in Watertown, a suburb of Boston. Tamerlan died after the gunfight, in which up to 250 rounds were discharged; his younger brother Dzhokhar was captured alive.

It remains unclear how the brothers obtained the Ruger, which had its serial number scratched off. But the existence of the gun, combined with the disclosure last week that in 2011 Tamerlan Tsarnaev was placed on a classified FBI watch list for suspected terrorists, has brought the so-called “terror gap” back into the political debate.

Under current laws, individuals can still buy weapons at gun shops even though a requisite FBI background check reveals that their name is stored on a central database of potential terrorists.

Can’t get on an airplane…can buy a semi-automatic weapon.

God Bless the U.S.A. NRA.