A prosecutor's spokesman says authorities believe they have identified suspects in the ambush at a western Pennsylvania cookout that left five adults and an unborn child dead, but arrests aren't imminent.

Mike Manko, spokesman for Allegheny County District Attorney Stephen Zappala Jr., says a task force is making progress in the investigation into the March 9 killings in Wilkinsburg.

Manko says investigators are "cautiously optimistic" they've identified the suspects. He says, however, that more work is needed and officials "do not expect any arrests to be imminent."

Investigators say one man fired a pistol from an alley at the backyard gathering, prompting the cookout guests to run toward a house for cover, where they were mowed down by another man with an assault rifle.