SHANKSVILLE, Pennsylvania - Investigators say they've found no indication of arson or other foul play in the fire that damaged buildings at the Flight 93 National Memorial in Pennsylvania.

Sweatshirts are on sale in the gift shop of the newly opened Flight 93 National Memorial in Shanksville, Pennsylvania, September 9, 2015. [Photo/Agencies]

A National Park Service spokesman said Sunday the investigation isn't over, and it may be weeks before officials determine the cause of the blaze that destroyed the memorial's headquarters.

The scene is now under control of park officials, who are doing what they can to salvage material left after the Friday fire.

An initial inventory indicated the losses included a flag that flew over the US Capitol on Sept. 11, 2001, the day four planes were hijacked.

Flight 93's passengers fought with the attackers before it crashed in western Pennsylvania.

The memorial and visitor center, under construction about 2 miles (3 kilometers) away, weren't damaged.