Philadelphia ? The National Park Service is investigating what went wrong at the opening of the National Constitution Center, where a large wood and steel frame tipped over, injuring several people and narrowly missing Supreme Court Justice Sandra Day O’Connor.

The apparent accident on Friday was being investigated to exclude the chance that sabotage or vandalism were to blame, officials said. The park service and museum said they would work together on the investigation.

The museum’s opening ceremony was to have ended when people on stage pulled on ribbons attached to a frame. A screen was supposed to drop, revealing a piece of artwork and officially opening the museum. Instead, the frame came crashing down.

Forty-two people were on the stage, and U.S. Sen. Arlen Specter and a federal judge suffered minor injuries. U.S. Supreme Court Justice Sandra Day O’Connor narrowly missed being hit.

“We had a great celebration, it was perfect right up until about the last 10 seconds,” Mayor John Street said Saturday on NBC’s “Today” show.

The new center holds exhibits, including the first public printings of the Constitution and an inkwell Abraham Lincoln used in signing the Emancipation Proclamation.

Supreme Court justices Antonin Scalia and Stephen Breyer and music legend Ray Charles also attended the ceremony but were not near the frame when it fell.

Philadelphia Liberty Medal recipient Supreme Court Justice Sandra Day O'Connor, center, watches as people lift part of a frame surrounding a mural that fell onto the dais during the closing of the Liberty Medal award ceremony at the new National Constitution Center in Philadelphia. O'Connor was narrowly missed, but not injured, Friday.