MIAMI (AP) -- Workers inched closer Thursday afternoon to pulling a fourth likely casualty from the site of a parking garage collapse as a search for answers continued over what reduced a routine construction project to piles of twisted steel and crumbled concrete.
Family members of a still-missing worker huddled near the site, a day after the collapse at Miami Dade College, waiting for a crane to remove large debris and potentially remove a body from an area search dogs had identified. Some still held out hope for a miracle, but authorities said they didn't expect to find anyone else alive.
A police officer who spoke with relatives at the site said that rescuers planned to search until nightfall Thursday, but that it could take days to find someone. When family members asked whether survival was possible, the officer tried to offer encouragement. Afterward, though, several turned their backs to the rubble and sobbed.
"We break down and we console each other," said Steve Budhoo, who identified his brother as the missing worker. "We are just going through the motions."
Earlier Thursday, a third worker succumbed to injuries from the collapse. Samuel Perez, 53, had been pulled from the piles of wreckage just hours earlier, after being trapped for about 13 hours. He was found after rescue workers heard his cries. Perez and the two other confirmed fatalities -- Jose Calderon and Carlos Hurtado de Mendoza -- all died at hospitals after being rescued and worked for subcontractors of the firm handling the construction of the five-story garage, Ajax Building Corp.
At least eight other workers were injured.
The accident happened, Ajax CEO Bill Byrne said, as crews were putting in a "spandrel beam" on the day of the collapse. The beam, a five-story, pre-cast concrete puzzle piece that was to attach to an elevator shaft, was still hanging from a crane near the wreckage Thursday.
Byrne said the project was utilizing pre-cast concrete construction, in which massive concrete pieces are created off-site and put into place by construction workers. Observers said the method has been around since about the 1950s and in recent decades has become the most common method of garage construction, largely because it is more cost-effective.
What precisely caused the accident, though, remained a mystery.
Al Brizuela, a Miami engineer who has worked on parking garage projects and who acts as a forensic engineering consultant, said any of a number of things may have gone wrong. In pre-cast structures, he said, concrete slabs have more flexibility than those that are poured on site.
"The last slab could have slipped, but the way the columns failed in the center, they basically exploded," Brizuela said. "It could be a combination of many factors -- it could be maybe an error of the design, an error in the construction of the columns."
The slabs of concrete easily weigh tons apiece. Workers are typically well aware of the risks when they're being positioned, and when something goes wrong, it's tough to survive.
"Any slight deviation in the alignment will cause a catastrophic failure," Brizuela said. "They had no chance, the guys that were underneath."
Joe White, an owner of Carl Walker Construction Inc., a Pittsburgh company specializing in parking garages, said he suspected the problem may have been there were too few welders to secure the concrete pieces together. Left unsecured, anything from a gust of wind to a tap from a crane could send a slab crashing over, White said.
"All they have to do is tap that thing and it just knocks that whole thing straight to the ground," he said.
Authorities have not yet identified any cause in the accident. Byrne said there was "no warning whatsoever."
Ground was broken on the $22.5 million project in February, and the 1,855-space garage was to be finished in December, according to Ajax's website. The first floor was to have classroom and office space. The structure is next to the main office building at the 8,000-student college and nestled among other campus buildings.
No students were in the accident area because the garage was under construction. The campus was evacuated and closed for the rest of the week. Officials said there was no visible damage to other buildings, but even a hairline fracture could compromise safety.
"Very concerning to us was that this facility was about to open," said Juan Mendieta, a spokesman for Miami Dade College. "Had this collapse happened just a couple of months from now, it would have been a totally different story. So for that reason, we're not going to leave a stone unturned."
Associated Press writer Freida Frisaro contributed to this report.