Or a Glock while being holstered with a finger still on the trigger. That's happened before and probably will again.
According to This Guns and Ammo article They FFDOs are issued HK USP40 Compact LEM (Law Enforcement Modification) pistol. Also several other articles, including this one from BNET Business network
Don't know which caliber that one is, they come in 9mm, .40 S&W and .45 ACP. (I want one!).\