Vance Boelter's disguise wasn't perfect. The silicone mask was somewhat loose-fitting and his SUV's license plate simply read "POLICE" in black letters. But it was good enough on a poorly lit suburban street in the dead of night.

When the gunman in the shootings of two Minnesota lawmakers approached their homes early on Saturday morning, he was armed with not just a handgun but also a wealth of other gear: a black tactical vest, a badge, a flashlight, a Taser. He arrived in a black S.U.V. with flashing police lights.