More details: “...police believe that the two men entered the four-unit apartment building at 23 Merritt Ave., fired through the door of the first-floor apartment and entered. She said a man and his girlfriend were inside, and the pair pushed the man into a bedroom, where he kept a shotgun. The man then shot the two intruders.”
Fired through the door implies the intruders were armed.
http://pittsburgh.cbslocal.com/2014/07/22/1-dead-1-critical-after-shooting-in-carrick/
While filming in Carrick, the product crew turned Merritt Avenue into Brady Avenue for the movie. (Which confused police.)