Federal investigators searched through the Dallas Cowboys' practice facility , hoping to find out what caused the huge bubble ceiling to cave in during a rookie workout session. The collapse sent 12 people to the hospital and left one man paralyzed from the waist down.
Inspectors from the Occupational Safety and Health Administration are back on the scene this morning to continue looking through the metal and canvas, trying to determine if the tragedy could have been avoided.
Was there a structural weakness in the training facility that caused it to buckle in those powerful 64-mile-per-hour winds?
An engineer said that the structure should have withstood the wind.
"I think it should have held. The basic windspeed for design in that part of Texas is 90 miles an hour," forensic engineer Gene Corley said.
Donato Fraioli, the CEO and chief engineer for Air Structures American Technologies, Inc., said the engineering of the frame nand the assembly of the structure need to be evaluated.
Pennsylvania-based Summit Structures put up the practice facility in 2003 and says everything was done properly.
ABC News has learned Summit was held liable for $4 million after a similar roof collapsed in Philadelphia in 2003 after it was overloaded with snow.
Sports teams at the University of New Mexico, Texas A&M and the New England Patriots use similiar facilities built by Summit.
The Cowboys got a building permit from the city for a new roof last fall after the old one was damaged, reports ABC News affiliate WFAA in Dallas-Fort Worth. Paperwork was filed with the city of Irving for repairs, but WFAA has learned city building inspectors never came to inspect the repairs and sign off on them.
Cowboys owner Jerry Jones has said the team didn't have any warning this was going to happen.
About 70 people, including 27 players at a rookie minicamp, were inside when the storm hit. Winds were clocked at 64 mph, one mph shy of the threshold for a weak tornado. The National Weather Service had issued a severe thunderstorm warning for the area and rookies kept practicing.
A "microburst" may have pushed the wind beyond 70 mph at the top of the structure, National Weather Service officials said.
Twelve people were hurt, including Cowboys special teams coach Joe DeCamillis, who was set for surgery Monday on his fractured cervical vertebrae. The most seriously hurt was Rich Behm, the team's 33-year-old scouting assistant who was permanently paralyzed from the waist down after his spine was severed. Greg Gaither, 35, had surgery on his fractured right leg and was expected to get out of the hospital this week.
The Associated Press contributed to this report.