Unstable rubble hampered efforts Friday to determine what caused a thunderous explosion that killed one person, injured several and leveled a downtown restaurant and a store in the southern Colorado city of Pueblo.

The mounds of rubble kept federal and state officials from getting a close look at the destruction to find possible causes of Thursday’s blast. Investigators wanted to inspect a natural gas line and a gas meter at the site of the restaurant, the Pueblo Fire Department said.

“We still don’t know exactly what happened,” department spokesman Gary Micheli said.

The investigation will include city arson investigators, agents from the Colorado Bureau of Investigation, and the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives.

“That’s not to say whether we suspect anything at this point in time,” said police Chief John Ercul. “It may be an accident.”

A gas leak was found in a street next to the destroyed Branch Inn restaurant and A Classic Boutique store. It wasn’t clear whether the pipe was ruptured by the explosion or contributed to it, Fire Department spokesman Woody Percival said.

The break was in a gas main about 20 feet from the point where a branch runs to the building that exploded. At least one witness reported smelling gas after the blast.

The explosion Thursday afternoon spewed glass, brick and other debris more than 100 feet and damaged buildings and cars. One survivor was found in the rubble more than four hours after the blast.

A 22-year-old woman who had been in the boutique died at Parkview Medical Center, Pueblo County Coroner James Kramer told The Pueblo Chieftain.

A 74-year-old man who was in the restaurant was in critical condition Friday at Parkview, police said. The 41-year-old co-owner of the Branch Inn was in fair condition, two of the injured had already been released and the condition of the others wasn’t clear, the Chieftain reported.

___

Associated Press writer Dan Elliott contributed to this report.