Two firefighters stand on the debris around the smoldering wreckage of the the three houses that exploded in Plum, Pa., on Aug. 12, 2023. Three houses at the center of a recent explosion near Pittsburgh that killed six people will need to be torn down and 10 others are not currently inhabitable, county officials said over the weekend. (Samuel Long/Pittsburgh Post-Gazette via AP, file)

PLUM, Pa. (AP) — Investigators say the location of an explosion that killed six people and destroyed three houses near Pittsburgh last month was inside one of the homes, and they’re ruling out an outside cause. The Allegheny County fire marshal’s office said Friday all potential outside factors were eliminated, including wells, pipelines and other utilities. They’re pinpointing the source as a home in Plum Borough. The cause of the explosion remains under investigation and they’re offering no time frame for when the probe will be completed. That house and two others are so badly damaged they must be demolished. All of the victims were found at the home.