PLUM, Pa. – The Allegheny County Fire Marshal said the Plum explosion that killed six people last month came from inside the house at 141 Rustic Ridge Drive. According to the fire marshal, several levels of testing have been conducted and completed since the start of the investigation, including all potential outside factors, like wells, pipelines, ground gas propagation and other utilities, which were all inspected and tested by each associated agencies and companies. The results of the testing confirm there are no factors outside of the house that led to the explosion, the fire marshal said. The property at 141 Rustic Ridge Drive will be turned back over to the property owners and representatives, the fire marshal said. Follow up interviews are still being completed with some first responders and witnesses. The cause of the explosion continues to be investigated.