(NBC News) -- Investigators are eyeing a broken clamp in a Ringling Bros. accident that sent a troupe of aerialists plunging 35 feet to the floor in front of a stunned audience, officials said Monday.
Lab technicians will examine the failed piece of equipment — D-ring carabiner — and other parts of the performers' apparatus to determine the cause of Sunday's mishap, which landed nine performers in a Rhode Island hospital.
Providence Public Safety Commissioner Steven Pare said investigators know at least one clamp attaching the "human chandelier" to the rafters at the Dunkin' Donuts Center failed.
It's unclear why it broke or if other parts of the complex rigging system malfunctioned.
Steve Payne, a spokesman for Feld Entertainment, the parent company of Ringling Bros. and Barnum and Bailey, said the circus' own investigation has not been completed.
"It's premature to go down that road and say whether that clamp was a contributing factor or not," he said.
The federal Occupational Safety and Health Administration is in charge of the probe, which has scuttled the rest of the Providence dates for the Ringling Legends tour. Performances in Hartford, Connecticut, begin Thursday.
Pare said two of the acrobats are still in critical condition; three are in serious condition and three are stable.
Two of them had surgery, including Widny Neves, 25, whose father told NBC News that it was a miracle everyone survived the collapse.
The fall was captured on video by a ticket-holder. It shows that after a curtain dropped, the performers began a ballet act while hanging from their hair about 35 feet from the floor.
Seconds later, the platform dropped unexpectedly and the performers, who were working with no net, plunged to the floor with it.
The rigging for the show was designed by the troupe's founder, Andre Medeiros, whose wife was in the air and is among the injured.
Jeffrey Feld, the circus' chief executive, flew into Providence last night to meet with the victims and their families, Payne said.