As of this writing, the top two hashtags trending on Twitter are #aurora and #theatershooting. The next trending phrase is "James Holmes," the name of the suspect whom the police have in custody. The broad details of the case are: there was a shooting in one of the theaters airing a midnight showing of The Dark Knight Rises. The shooter came in through the emergency exit, and threw in a canister of what is believed to have been tear gas before opening fire. He was wearing a bullet proof vest and a gas mask. Police are searching James Holmes's apartment, because he claimed to have explosives.
Because I don't know what's going on in Colorado right now, I don't know how certain they are that James Holmes is the right guy -- so I want to stress that the police are holding him as a suspect, he hasn't been convicted of anything.
12-14 people are dead. 38-50 have been injured.
Here are my sources, for further information.