When the police received a tip that Dzhokhar Tsarnaev might be hiding out in a Watertown boat, there was obviously some worry: how do you safely check to see if he's there when he's been carrying explosives this whole time? You use a police helicopter's thermal camera, of course. 

On Saturday, the Massachusetts State Police released these pictures of a Dzhokhar Tsarnaev holed up in David Henneberry's boat Friday evening before the firefight with police and subsequent arrest. They were taken using the state police's Forward Looking Infrared (FLIR) cameras on their Air Wing helicopters, and they really are something:

Basically, the cameras on the state helicopters allow state police to read thermal energy. So if someone is hiding behind, say, a boat tarp then they're able to read his body energy and verify a target's location. "FLIR cameras allow the TFO to see in total darkness by producing viewable images of invisible infrared energy," explains AOPA Hover Power writer Tim McAdams. "Infrared energy is part of the electromagnetic spectrum, which we perceive as heat, so it is invisible to the naked eye. Some level of thermal energy is emitted from all people, objects, and material." The police can see your warmth, criminals. They're hot on your trail.