The flag that flew over the United States Capitol on Sept. 11, 2001, was among several artifacts destroyed in a fire at the headquarters of a memorial in Pennsylvania to victims of the crash that day of a hijacked jet there, the National Park Service said on Saturday.

The flag was being stored at the headquarters of the Flight 93 National Memorial in Shanksville, in southwestern Pennsylvania, after Dennis Hastert, the former House speaker, donated it during a remembrance ceremony last month for the 40 victims aboard the United Airlines jet.

The headquarters building and some personal items belonging to the passengers and crew were destroyed in the fire on Friday, but the vast majority of the memorial’s collections were unharmed. The Park Service and the Pennsylvania State Police are investigating the cause of the blaze.