YORK, Pa. — Federal investigators say the cause of a Pennsylvania fire that preceded a building collapse that killed two firefighters remains undetermined, but there is no indication that it was deliberately set.

Donald Robinson of the Bureau of Alcohol, Tobacco, Firearms and Explosives said Friday his office has wrapped up its portion of the investigation.

Robinson said the fire started on the first floor, and several potential accidental causes of the fire will be taken for testing and analysis. He said officials have no evidence that anyone was in the building when the fire started.

Fifty-year-old Ivan Flanscha and 29-year-old Zachary Anthony were killed last week in a wall collapse as they were looking for hot spots from a fire the day before at the former piano factory in York.