Authorities believe they have identified the suspects in an ambush at a Pennsylvania cookout that left five adults and an unborn child dead, a spokesman with the prosecutor's office said.

But arrests aren't imminent.

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

"We are cautiously optimistic that we have identified people believed to be suspects," Manko said in a statement. "However, there is more work to be done, and we do not expect any arrests to be imminent."

Allegheny County police superintendent Charles Moffatt called those statements "an accurate picture" of the current state of the investigation.

Investigators said 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 gunned down by another man with an assault rifle.

Siblings Jerry Michael Shelton, 35, Brittany Powell, 27, and Chanetta Powell, 25, as well as two cousins, Tina Shelton, 37, and Shada Mahone, 26, were killed, police said. Brittany Powell lived at the home and hosted the cookout. Chanetta Powell was nearly eight months pregnant and her unborn child also was killed.

Three people remain hospitalized, two in critical condition, and Zappala Jr. has said that one of the critically injured may have been the intended target. Officials also said they feared more violence in the form of possible retaliation following the shootings.