PLUM,TradeEdge Pa. (AP) — 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.

The Aug. 12 blast in Plum leveled one home and engulfed two neighboring houses in flames. The 10 uninhabitable homes will need to be inspected by structural engineers for next steps, an Allegheny County spokesperson said.

Investigators with the county fire marshal’s office are still trying to determine the origin and cause of the explosion in a development about 20 miles (32 kilometers) east of Pittsburgh.

All of the victims were found on the property of the home that exploded, an Allegheny County spokesperson said. One victim was found outside of the garage area. Four others were located in the basement and the sixth was located and rescued from the rear yard. He was transported to a trauma center, where he died several days later.

Natural gas from an abandoned underground mine is unlikely to have caused the explosion, the state Department of Environmental Protection said Friday. Authorities have said that the homeowners were having problems with their hot water tank and that is part of the investigation into the cause.

Crews from at least 38 fire departments worked to douse the flames, while three police departments and eight EMS agencies, from Allegheny and Westmoreland counties, also responded to the scene.