(CNN) -- Two days before a bridge crumbled in Miami, killing six people, an engineer for the company that designed it called a Florida Department of Transportation employee, warning of "some cracking."

The state employee was out on assignment that day. The call from W. Denney Pate of FIGG Bridge Engineers was unanswered, and the voice mail he recorded unheard -- until Friday.

In the voice mail, Pate said the cracking on the north end of the span should be repaired. However, he added, there were no safety concerns on the project near Florida International University.

"We've taken a look at it and, uh, obviously some repairs or whatever will have to be done," Pate said.

    "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."

    It's too early to tell whether the bridge failed when construction workers were applying post-tensioning force to strengthen the beams, said Robert Accetta of the National Transportation Safety Board.

    Accetta said a crack in the bridge "does not necessarily mean that it is unsafe."

    Sen. Bill Nelson is asking for documents related to the "engineering, design, construction, safety and inspection."

    "In light of the fact that there were multiple agencies and companies involved, we're going to need a clear understanding of who had what role in this horrible tragedy," he said in a statement.

    The bridge was supposed to enhance safety and keep pedestrians safe from traffic in the busy eight-lane street. On Thursday, it collapsed, months ahead of it's completion.

    In an instant, the bridge crushed the cars below, trapping an unknown number of people and injuring others.

    Among the six killed is 18-year-old Alexa Duran, her father told el Nuevo Herald.

    The FIU student was driving under the bridge Thursday when it crashed down. A friend traveling with Duran tried to pull her out but he couldn't.

    "My little girl was trapped in the car and couldn't get out," Orlando Duran said.

    Ecuador's foreign minister Maria Fernanda Espinosa confirmed Duran's dead in a tweet and said she was the "daughter of an Ecuadorian father."

    It's unclear whether Duran's body has been recovered. Of the six people who died, five bodies remained under the wreckage Friday, Miami-Dade police spokesman Alvaro Zabaleta said.

    Authorities have not identified any of the victims and have said crews may find more people as they continue digging through the rubble.

    Others have desperately waited for nearly 48 hours for word on their loved ones.

    Jorge Fraga has visited the local hospital, called the Red Cross and tried to get close to the debris looking for his 60-year-old uncle.

    "I want to find out for sure if it's him out there," Fraga told CNN affiliate WPLG. "They saw the car -- his Cherokee. We don't know exactly his whereabouts."

    Barbie Brewer, a victims advocate for the Miami Dade Police Department, told CNN affiliate WPLG that most families are hopeful.

    "They just want to believe that their families are still alive," she said.

    The under-construction bridge was meant to connect the FIU campus to the Sweetwater neighborhood, home to more than 4,000 of its students. FIU is the second-largest public university in Florida, with about 50,000 students.

    The 174-foot main span had been assembled on the side of the road, allowing traffic to continue. On March 10 -- at the start of FIU's weeklong spring break -- a rig moved the span into position over the street as community members gathered to watch. The process took about six hours.

    The bridge was scheduled to open to foot traffic in 2019, and was designed to boost safety on busy 8th Street, where an 18-year-old FIU student was fatally struck by a vehicle in August.

    MCM, a construction firm building the bridge, and FIGG Bridge Engineers, said they'll conduct an investigation and are cooperating with investigators

    A spokesman for MCM told CNN the company has had $152 million in federally funded government projects in the past five years. Federal contract data shows that since 2013, MCM has been awarded about $130 million worth of contracts from the Army and Navy for various construction, maintenance and repair projects. Documents show it was involved in bridge projects nationwide.

    At least one MCM project resulted in a lawsuit concerning safety, CNN has learned. Records show the Occupational Safety and Health Administration cited MCM for 11 violations involving construction projects in Miami and Hialeah, Florida, between 2014 and 2017.

    The OSHA violations included citations for employees not receiving proper hazardous-chemicals training before handling concrete, not removing water from excavations and not wearing safety glasses and protective gloves, documents show.

    The reason behind Thursday's collapse remains a mystery and the company has said it will conduct a full investigation.

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