Police near Pittsburgh are seeking to identify suspects in a deadly ambush attack by two men who methodically shot and killed five people, including a pregnant woman, at a backyard cookout.

A prosecutor says the gunmen appeared to have targeted one or two of the victims. District Attorney Stephen Zappala says drugs haven't been ruled out as a motive.

One man and four women were fatally shot. Officials ruled the death of the pregnant woman's fetus a homicide on Thursday, raising the death toll to six.

A man opened fire on the partygoers Wednesday night, driving them in the direction of an accomplice who gunned them down with a rifle.

Police have no suspects and a county executive is urging witnesses to come forward.