This article is by Mary Ellen Klas, Andres Viglucci and David Ovalle.

Cracking in the concrete, tension cables, stress tests — no conclusion has been made whether any of them caused the pedestrian bridge at Florida International University to collapse, killing six motorists under an avalanche of concrete and metal.

But as crews continued working Saturday to recover the last victims from the rubble, finger-pointing over the tragedy escalated between the university and the Florida Department of Transportation, which swiftly moved to distance itself from the tragedy despite its integral role in the project.

"We've had a good relationship with FDOT — I just want to make it clear," FIU President Mark Rosenberg told the Miami Herald late Friday. "So we're anxious to find out more about what they think we didn't do. Because they've been involved at every step."

The public war of words unfolded throughout the day as police released the identities of the dead victims and state and federal authorities ramped up their investigation into the failure of the unfinished bridge, designed to provide a beautiful walkway from the FIU campus to downtown Sweetwater, where many students live.

The National Transportation Safety Board, Miami-Dade homicide detectives and prosecutors are focusing on the government agencies and two contractors — Munilla Construction Management, which was building the structure, and FIGG Bridge Group, which engineered and designed the span.

Designed as a quick-build project, the 950-ton concrete main span was assembled off site, part of a strategy to minimize disruptions to traffic, and placed over the state road in a single morning one week ago. The bridge was not scheduled to open until 2019.

On Thursday afternoon, after work that reportedly comprised "stress tests" and tightening of structural cables was conducted while motorists streamed underneath, the structure collapsed in horrifying fashion. New footage of the collapse, taken from a vehicle dashcam and posted to the Internet, suggests the concrete came apart on the north end — the same area where the bridge's design engineer told the state on Tuesday that cracking had been discovered.

FIGG said that "based on the best available information," there was no safety issue with cracking discovered on the structure days before the collapse. What precisely caused the bridge to crumple remains very much an open question, independent experts say.

Read more: Bridge designer left FDOT voice mail about cracks days before FIU bridge collapsed

While the cracking dominated media coverage on Saturday, experts appeared less concerned over that than with other factors, including the tensioning work going on at the bridge's north end. Cracking in new concrete is not uncommon and not necessarily a sign of failure, they say.

Tightening of steel cables, or tendons, that run through concrete structural elements is a delicate operation, and over-tightening can cause concrete pieces to twist and break apart, experts say.

Without knowing more, it's hard to say whether the cracking found Tuesday was significant, said Martin Gordon, president of the National Academy of Forensic Engineers and a professor at the Rochester Institute of Technology.

"You don't know where the crack was. You can speculate all you want," Gordon said, adding, "If the crack was near the truss member that they were tightening, then that obviously might not have been a good idea to be doing work near that crack. You have to err on the side of caution."

Former FIU President Mitch Maidique, an engineer who was not involved in the project, said a catastrophic bridge failure of this kind is usually the result of multiple problems, not a single cause.

"My experience is that when something goes wrong it's rarely the result of one thing that went wrong," Maidique said. "It is typically multiple failures, because systems are generally designed with backups. It's too early to tell. But my guess is when the autopsy is completed, you'll find multiple sources of errors that led to this disaster."

Public blame-shifting among those involved in the project started within hours of the collapse on Thursday. FDOT — led by an appointee of Gov. Rick Scott — issued a "fact sheet" insisting that the agency's role "was limited to" traffic-control permits, administering funding and authorizing FIU "to utilize the aerial space above the state road."

"It was not a FDOT project. It was an FIU project," Scott told reporters the night of the accident. "There will clearly be an investigation to find out exactly what happened, and why this happened. We will hold anybody accountable if anybody has done anything wrong."

Then, on Friday night, FDOT followed up with two more bombshells. That it had no idea any "stress tests" were being conducted over the busy thoroughfare next to the West Miami-Dade campus, which might have required permits for a road closure.

And that W. Denny Pate, a FIGG engineer, discovered cracking in a north portion of the concrete span. He left a voice mail for an FDOT employee two days before the collapse.

"We've taken a look at it and, uh, obviously some repairs or whatever will have to be done but from a safety perspective we don't see that there's any issue there so we're not concerned about it," Pate said in a voice mail released by FDOT.

The voice mail message was not received until Friday — the day after the collapse.

The press release also noted a meeting that took place between the FIU team and FDOT hours before the collapse — but left out any mention of whether cracking at the north end of the structure was discussed. An FDOT employee on hand "was not notified of any life-safety issues, need for additional road closures or requests for any other assistance" from the state agency.

But on Saturday morning, FIU issued its own press release, saying FDOT knew about the crack — because it was the whole point of calling the meeting, held in a trailer office at the construction site.

"The FIGG engineer of record delivered a technical presentation regarding the crack and concluded that there were no safety concerns and the crack did not compromise the structural integrity of the bridge," the school statement read. "This meeting lasted approximately two hours and included FIU and FDOT representatives."

FDOT responded again, this time to minimize the role of its consultant, engineer Alfredo Reyna, who attended that meeting. The agency said his role was administrative — to ensure the project is on schedule and remains qualified for federal funding.

Read more: 'Beyond tragic': Miami congressmen shaken by FIU bridge collapse

"The responsibility to identify and address life-safety issues and properly communicate them during this project is the sole responsibility of the FIU design build team," FDOT said in a follow-up release Saturday afternoon.

For all the hand-wringing over the cracking that appeared in the bridge, it's unclear if or how it contributed to the tragedy.

Experts say it is not unusual for cracks to appear in a project. Their conjectures have focused on several elements, including the cable-tensioning work, the unusual design of the quick-build bridge, the lack of temporary shoring, and the decision to carry out testing and tightening of structural elements while the road was open to traffic.

Some independent engineers also questioned why a system consisting of a pylon and cable-like support pipes that's part of the bridge design was left for later. Usually in suspension bridges, the pylon is built first.

But design documents and descriptions on FIU's website say the pylon was not meant as the principal means of support for the bridge span, which was designed to hold up by itself. Instead, the pylon system was to provide stiffness to the structure, lessen vibration for pedestrians and provide aesthetic bang.

Still, some experts questioned the decision to leave it for last. If the pylon and stays had been in place, the structure may have had redundant support to keep it stable even if another structural element failed — during cable tensioning, for instance. Over-tightening can cause concrete beams and struts to twist and crack.

The pylon would have been located at the end where dashcam video suggests the bridge came apart, Gordon noted.

"What struck me was that the collapse occurred in an area of the bridge where the pylon would have provided the most vertical support," Gordon said, while stressing that he is an aerospace structural specialist but not a bridge expert. "I can't help but feel the pylon would have increased the factor of safety.

"It's looking like someone may have been a little overconfident. I tell my students you never want to design something that would kill someone unintentionally. You always want to go with your worst-case calculations," he said.

NTSB Chief Investigator Robert Accetta told reporters Friday it was too early to say whether cracks played a role in the FIU bridge collapse. He also said the presence of cracks is not necessarily a red flag for safety.

"I would have to say that a crack in the bridge does not necessarily mean it's unsafe," he said, though NTSB investigators made it clear that they had not confirmed whether there were cracks. "That's still too early in the investigation for us to determine."

Miami Herald reporters Doug Hanks and David Smiley and el Nuevo Herald reporter Nora Gámez Torres contributed to this report.