5:58pm ET Update: Despite previously ruling out a gas explosion, the Charlotte Fire Department said that was “caused by an internal gas leak.”

“Off site investigators” will continue to investigate what triggered the explosion, according to WSOCTV’s Joe Bruno.

A home in Charlotte, North Carolina was leveled by an explosion Tuesday morning, and 24 hours later, investigators are looking for answers.

Dr. Jebran Karam, one of the homeowners, was airlifted to the emergency room after calling police from the scene. He was trapped under the rubble for three hours before firefighters could pull him out, according to WSOCTV. A woman named Rania Karam, believed to be Dr. Karam’s wife, died during the explosion.

Dr. Karam was the only survivor. He is a cardiologist who reportedly works in West Virginia, and authorities that he “has no idea what happened.”

Fox46 confirmed that the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) has been called in to investigate the scene. Authorities have not ruled out foul play.

The explosion was so massive that it reduced the 6,500 square foot, $1.2 million home to rubble and sent shockwaves through the neighborhood. Neighbors reported thinking that their own homes had exploded. Debris damaged nearby homes.

A gas explosion has been ruled out by Piedmont Natural Gas. The company said:

“We are deeply saddened by the tragic loss of life. Our condolences and prayers are with those who are injured and who’ve lost a loved one.

Yesterday, our technicians tested and checked the Piedmont natural gas lines in the area, and no natural gas leaks on our lines were detected. We’ve determined the Piedmont natural gas pipelines in this area are operating safely. In an update last night, the fire department confirmed the area is safe.

Piedmont Natural Gas is committed to assisting and cooperating fully with the fire department and other agencies investigating this tragedy. The safety of this community continues to be our highest priority.” 

Firefighters battled the blaze for hours in the heat, with neighbors bringing them Gatorade, pizza, and watermelon to help sustain them.

A press conference is being held at 4:00pm Eastern to provide an update.

The Charlotte-Mecklenburg Police Department did not immediately return a comment request.