Updated at 10:05 p.m. ET

Florida transportation officials say that an engineer with the private firm that designed the concrete bridge that collapsed Thursday called the state two days before the incident to report cracks in the structure.

It's not immediately known whether the reported cracks contributed to the collapse of the pedestrian walkway that was intended to join the campus of Florida International University and the city of Sweetwater.

The Florida Department of Transportation released a transcript of a voicemail left on Tuesday March 13, by W. Denney Pate, lead engineer with FIGG Bridge Engineers, a Tallahassee firm.

"'Hey Tom, this is Denney Pate with FIGG bridge engineers. Calling to, uh, share with you some information about the FIU pedestrian bridge and some cracking that's been observed on the north end of the span, the pylon end of that span we moved this weekend. Um, so, uh, 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 from that perspective although obviously the cracking is not good and something's going to have to be, ya know, done to repair that. At any rate, I wanted to chat with you about that because I suspect at some point that's gonna get to your desk. So, uh, at any rate, call me back when you can. Thank you. Bye.'"

According to a FDOT statement, the voicemail was not heard by an agency employee until Friday, March 16, after he returned to his office from an assignment. The bridge collapsed on Thursday.

The FDOT statement does not identify "Tom," the employee with whom Pate was attempting to share his information.

FDOT also noted that the university, FIU, bore the responsibility for the bridge's construction.

"The responsibility to identify and address life-safety issues and properly communicate them is the sole responsibility of the FIU design build team. At no point during any of the communications above did FIGG or any member of the FIU design build team ever communicate a life-safety issue. Again, FIGG and the FIU design build team never alerted FDOT of any life-safety issue regarding the FIU pedestrian bridge prior to collapse."

The engineering company Figg said in a statement that it is working with authorities to determine the cause of the collapse.

"We are heartbroken by the loss of life and injuries, and are carefully examining the steps that our team has taken in the interest of our overarching concern for public safety. The evaluation was based on the best available information at that time and indicated that there were no safety issues. We will pursue answers to find out what factors led to this tragic situation, but it is important that the agencies responsible for investigating this devastating situation are given the appropriate time in order to accurately identify what factors led to the accident during construction."

Search-and-rescue teams have been carefully unearthing bodies and vehicles from under the concrete bridge that collapsed suddenly in Miami on Thursday afternoon. Questions about the bridge's design and construction are just beginning.

The 174-foot, 950-ton main span had been lifted into place just five days earlier. At least six people were killed and 10 were injured in the collapse, according to The Associated Press.

On Thursday night, Florida Sen. Marco Rubio tweeted: "The cables that suspend the #Miami bridge had loosened & the engineering firm ordered that they be tightened. They were being tightened when it collapsed today."

Because the bridge's central tower and suspension cables were not yet installed, the Miami Herald notes, any cables being tightened were likely wires that ran through the span.

The bridge was supposed to make the crossing of a perilous seven-lane roadway safer for students and staff at Florida International University. The bridge connected the university campus to the small suburban city of Sweetwater, where many students and faculty live. An FIU student was killed crossing the road in August.

Rubio is an adjunct professor at the university. His spokeswoman told the newspaper that he had heard this information from workers on-site.

At a news conference on Friday morning, assembled authorities would not confirm Rubio's statement.

"This is a tragedy we don't want to reoccur anywhere in the U.S.," said Juan Perez, director of the Miami-Dade Police Department. "Right now, we just want to find out what occurred, what caused this collapse to occur and people to die."

Representatives from the National Transportation Safety Board and the Occupational Safety and Health Administration are investigating.

"The people of South Florida have been though a lot, obviously, over the last several weeks and this is just yet one more tragedy to add to that sad book," said NTSB Chairman Robert Sumwalt.

Authorities said their investigation will take time, but early questions have emerged about whether it was wise to install the span across the road without first installing the central support tower.

Witnesses told WLRN the span fell without warning as a traffic light went red. Two workers were on the bridge when it collapsed, according to witnesses interviewed by the Miami Herald.

Last weekend, FIU tweeted a photo of what the completed bridge would look like.

As USA Today reports, the design was for a type of suspension bridge called a cable-stayed bridge:

"Cable-stayed bridges have cables attached directly from the column to the span, while suspension bridges string cables between towers and have other cables descend to the span."Amjad Aref, a professor at University of Buffalo's Department of Civil, Structural and Environmental Engineering, said a suspended bridge is typically built gradually, with the center tower or towers erected early."Pictures from the scene of the collapse don't show a central tower." 'Whoever is going to investigate, they will ask the fundamental question: shouldn't the tower be there, and the cables ready to connect to the structure, when you lift it?' Aref said. 'That's a question for them to answer.' "

FIU offers an entire program around bridge projects like this one: the Center for Accelerated Bridge Construction, which opened in 2011. "This method of construction reduces potential risks to workers, commuters and pedestrians and minimizes traffic interruptions," the university said in a press release when the span was swung into space last weekend.

Much of the funding for the $14.2 million bridge and its plazas and walkways came from a U.S. Department of Transportation grant.

The bridge was designed by FIGG Bridge Engineers and built by MCM Construction. Both companies have been involved in bridge collapses before, as the AP reports:

"FIGG was fined in 2012 after a section of a bridge it was building in Virginia crashed onto railroad tracks and injured several workers, according to a story in The Virginian-Pilot."MCM, meanwhile, was accused of substandard work in a lawsuit filed this month by a worker injured when a makeshift bridge MCM built at Fort Lauderdale International Airport collapsed under his weight. Another dispute resulted in a $143,000 judgment against MCM over an 'arguable collapse' at a Miami-Dade bridge project."A review of OSHA records, meanwhile, shows MCM has been fined for 11 safety violations in the past five years totaling more than $50,000 after complaints involving its Florida work sites."Both companies expressed condolences for the victims and promised cooperation with investigators."Copyright 2018 NPR. To see more, visit http://www.npr.org/.