MEP Structural, based in Coconut Creek, Fla., was serving as the project's inspector, working as a contractor to the school. Contacted by ENR, the company declined comment.

Damaged Crane and a Crack

During a press event, Byrne said the crawler crane used to erect the spandrel beam had been damaged when it struck one of the building's columns on Oct. 8. The crane was repaired and recertified within two days, he says, and the column was deemed to be undamaged.

After the collapse, Anthony Williams, a worker on the job, told CBS News and the Associated Press that he had seen a crack on the fifth floor of the structure just prior to the collapse.

In response to that report, Byrne issued a statement, which read in part: "While we appreciate all information and feedback, it is extremely important to avoid speculation. This investigation needs to be based on facts.… Our number-one priority is to determine the cause of this accident."

Nam Shiu, a senior vice president with the restoration division of Walker Parking Consultants in Chicago—and who has investigated collapses—agreed it is too early to determine a cause.

"A variety of different issues could affect the stability of the erected structure," Shiu says. "There's no common cause."

The sequence in which the structure collapsed could prove key to investigators as they "try to put the jigsaw puzzle back together," Shiu adds.

A report from the Occupational Safety and Health Administration is expected within six months.

This file was updated to clarify the firms responsible for various components of the structure's design.