PLUM BOROUGH, Pa. — (WPXI) – Allegheny County District Attorney Stephen Zappala visited the site of that deadly home explosion in Plum on Wednesday. Zappala told our news partners at Channel-11 that it appears to be a tragic accident, but he said he still has a lot of questions about the magnitude and the intensity of that massive and deadly explosion, and he plans to bring in explosive experts to help the fire marshal with the investigation. Since 2008, there have been three separate explosions, and Peoples Natural Gas said so far they’ve found no connection between any of them. Zappala said investigators are concentrating on the hot water heater in the basement of home where the explosion originated. Two other nearby homes were destroyed by the blast and fire. Another dozen homes were damaged. Zappala says he will continue to monitor the investigation and he plans to meet with Peoples Gas to see what more can be done to put residents in Plum at ease.