By Nicole Chavez and Jason Hanna, CNN

(CNN) -- Three bodies were removed Saturday from the site of this week's collapse of an unfinished pedestrian bridge in South Florida, and workers who've toiled day and night to find them hope to recover the rest by the end of the day, officials said.

Authorities have said they believe at least six people were killed in Thursday's collapse near Florida International University, including the three recovered Saturday and one who died in a hospital.

Miami-Dade police have identified four of the people killed: Rolando Fraga Hernandez; Oswald Gonzalez, 57; Alberto Arias, 53; and Navarro Brown.

The bodies of Fraga Hernandez, Gonzalez and Arias were recovered from crushed vehicles that workers extracted Saturday morning, police said.

The family of FIU student Alexa Duran has said that she was killed in the collapse, but police have not named her as being among the dead.

Miami-Dade County Deputy Mayor Maurice Kemp cautioned Saturday that the final death toll won't be known until all the vehicles are removed.

Workers covered the crumpled cars with tarps and placed them onto flatbed trucks that took them away.

Crews were "paying respect with a moment of silence" before sending them to the medical examiner's office, Miami-Dade police Director Juan Perez said.

"It's going to be a long process" to remove the remaining vehicles, Perez said, "because (of) the ... weight and size of the structure that is laying on top of these vehicles."

Late Saturday morning, officials said four vehicles remained smashed under the rubble. Workers hoped to free them by Saturday night, Perez said.

Engineer reported crack 2 days before collapse

The bridge was supposed to enhance safety and keep pedestrians safe from traffic on busy Southwest Eighth Street, where a vehicle fatally struck an FIU student in August.

But the span collapsed Thursday, months ahead of its completion, crushing the cars below and trapping an unknown number of people and injuring others.

On Tuesday, two days before the span fell, 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 went unanswered, and the voice mail he recorded unheard -- until Friday, the day after the span fell.

In Tuesday's 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.

"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 of Florida is asking the US Department of Transportation 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," Nelson said in a statement Friday.

Searching for loved ones

Authorities have said crews may find more people as they dig through the rubble.

Among the six killed is 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 but couldn't pull her out.

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

Ecuadorian Foreign Minister Maria Fernanda Espinosa confirmed Alexa Duran's death in a tweet and said she was the "daughter of an Ecuadorian father."

It's unclear whether Duran's body has been recovered.

Bridge was to connect campus to neighborhood

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

The university used Accelerated Bridge Construction technology to build the bridge. Unlike traditional methods of construction, it streamlines the building process so that bridge projects can be completed quicker and more cost effectively.

The 174-foot main span had been assembled on the side of the road, allowing traffic to continue. On March 10, 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.

FIU has been on spring break this week, but classes will resume as scheduled on Monday. Counseling services will be available for students, faculty and staff, the school said.

The university's Student Government Association is planning to hold a vigil for the victims Wednesday morning at a campus facility.

Safety concerns

Munilla Construction Management, or MCM, a construction firm building the bridge, and FIGG Bridge Engineers said they 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 show that since 2013, MCM has been awarded about $130 million worth of contracts from the Army and Navy for 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. 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.

The-CNN-Wire

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