MIAMI -- Isabella Carrasco heard it before she saw it.
As she drove by Florida International University on Thursday afternoon, she noticed the newly installed pedestrian bridge just ahead and mentioned to her boyfriend beside her that construction on the span had been clogging the area.
They turned off busy 8th Street. And that's when Carrasco heard a loud bang.
"We thought maybe someone had hit us or we had hit somebody else. We looked back and the bridge had completely collapsed," Carrasco said.
"Quite frankly, I'm lucky to be alive. That could have easily been me and my boyfriend under that bridge had we not turned right and decided to stay at the light and gone a different direction."
Waiting at a red light one intersection away, Sweetwater police Sgt. Jenna Mendez had a firsthand view of the bridge's collapse. She initially thought a demolition crew did so intentionally.
"Why would they have brought the bridge down during the day?" she thought.
Then came a startling realization: "This was not on purpose," she said. "This was a catastrophe."
Mendez jumped out of her car, rushed to help and found four badly injured construction workers. Two had broken bones. One had a major cut to the head, and one wasn't breathing.
"I started yelling to civilians in the crowd, 'Please get me doctors. ... I need help up here.' A doctor jumped up, and she started helping," Mendez said.
Carrasco and Mendez, one ahead of the bridge and one behind it, were just two witnesses to a startling human-made disaster in Miami that took the lives of six people, including a student, a construction worker and several unlucky motorists who were in the wrong spot at the wrong time.
By Sunday the bodies of all six victims had been identified. Most were caught under 950 tons of steel and concrete that fell with enough force to flatten vehicles into pancaked hulks of metal.
The footbridge was built to avoid another tragedy.
Last August, an 18-year-old FIU student died when she was struck by a vehicle while crossing 8th Street nearby.
The university commissioned the $14.2 million bridge to avoid another such death and to connect the school's campus to the nearby Sweetwater neighborhood, where thousands of students live.
Designed by FIGG Engineering-Bridge Group and built by MCM Construction, it was on track to open in early 2019. Officials did not want to block the roadway for an extended period, so the bridge was built using Accelerated Bridge Construction (ABC) technology, a streamlined process that is quicker and more cost effective.
The bridge was intended to be strong enough to withstand a Category 5 hurricane and durable enough to last 100 years, the university boasted in a fact sheet.
The main span of the bridge, 40 feet wide and 174 feet long, was built on temporary supports alongside 8th Street. On March 10, the span was carefully lifted into place over the street.
Atorod Azizinamini, chair of FIU's Civil & Environmental Engineering Department and director of the university's Accelerated Bridge Construction University Transportation Center, praised the method of the bridge's construction in a statement five days before the collapse.
"This project is an outstanding example of the ABC method," said Azizinamini. "Building the major element of the bridge -- its main span superstructure -- outside of the traveled way and away from busy Eighth Street is a milestone."
A worrisome crack
But shortly after the span was installed, W. Denney Pate, a FIGG engineer, noticed a problem. A crack had formed on the north end of the span, and it needed to be repaired.
"We've taken a look at it and ... obviously some repairs or whatever will have to be done," Pate said in a voicemail for a Florida Department of Transportation employee on Tuesday.
"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."
That foreboding voicemail, left on Tuesday, went unheard until Friday, a day after the bridge collapsed. The state employee was out on assignment.
Other engineers also discussed the structural integrity of the span -- and deemed it safe -- just hours before it collapsed.
Representatives from FIU, the Florida Department of Transportation, Munilla Construction Management and FIGG Bridge Engineers attended a two-hour meeting Thursday morning to assess the span and the cracking.
"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," Florida International University officials said Saturday in a statement.
Robert Accetta of the National Transportation Safety Board said the crack "does not necessarily mean that it is unsafe."
An investigation over the next few months will determine exactly how the bridge failed.
"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," FIGG Bridge Engineers said in a statement. "The evaluation was based on the best available information at that time and indicated that there were no safety issues."
A sound like 'multiple bombs'
For Giovanni Hernandez, the collapse was more like an explosion.
"(It) sounded like a bomb, like multiple bombs in one," Giovanni Hernandez told WSVN. "It sounded like the world was ending, and when you look back, all you see is the bridge on the floor."
Sgt. Mendez, who rushed to help those trapped, said she can't recall the sound.
"When I look back and see the news stories, you obviously can hear all the horns and the chaos, and think I was in such a zone and a mode that I do not remember hearing anything, to be honest with you," she said.
But she remembered another sound: crying.
"We were trying to comfort (the survivors)," she said. "They were all pretty much in shock. Nobody was talking to us or answering our questions. We were aware that they were in shock, so we just kind of waited a good 15 minutes for them to start coming out of it and realizing what was going on."
Like Sgt. Mendez, witness Lynell Collins ran into the chaos to help pull people from crumpled cars.
"After the whole thing broke, I was freaking out," Collins told CNN. "I got out of my car, and me and a few other people were sprinting over there. We started helping people whose cars were at least half crushed and whoever was easily saved. But we couldn't really go under any of the rubble because, at the time, the bridge -- the other half of the bridge is still kind of leaning upward right now."
Collins said one of the victims said his family was still trapped beneath the rubble. No one could help get them out, the victim said.
'My little girl was trapped'
Alexa Duran, an 18-year-old FIU student, was driving a gray Toyota 4Runner when the bridge came down and pinned her underneath. A friend traveling with Duran tried to pull her from the wreckage but was unsuccessful.
"My little girl was trapped in the car and couldn't get out," her father, Orlando Duran, told El Nuevo Herald, a sister newspaper to The Miami Herald.
Authorities weren't able to remove her body from the mass of concrete and steel until Saturday afternoon. Several other victims were also trapped under the debris until Saturday.
Oswald Gonzalez, 57, and Alberto Arias, 53, were pulled from a crumpled white Chevy truck on Saturday, authorities said. Arias and Gonzalez were life partners and co-owned a party planning business together, according to Kary Lizano, a friend. They were a "great, loving couple, generous to the community," she said.
The body of Rolando Fraga Hernandez was found inside a gold Jeep Cherokee that was pulled out of the rubble on Saturday morning, police said.
Brandon Brownfield was killed in the bridge collapse, according to his wife, Chelsea Brownfield. He was a crane technician for Maxim Crane, but he was not working on the bridge and happened to be driving by when it collapsed. In a Facebook post, Chelsea Brownfield said they had been married for almost 4 years and have three girls.
Brownfield's friend and co-worker Ryan Lee said in an email to CNN that he was a family man and was dedicated to his wife and daughters.
"Brandon was the husband and father that we should all endeavor to be," Lee said. "Brandon will be sorely missed by all who had the opportunity to know him or to interact with him on the job. He was a true professional, a master of his trade, and a wealth of knowledge."
Navarro Brown, 37, was working on-site at the bridge for Structural Technologies VSL, which specializes in bridge cable tension and construction systems, the company told WTVJ. After the bridge collapsed, he was taken to a hospital and died there, police said.
Prayers for the victims
Rescuers at the site worked day and night to extract the dead.
On Saturday, for the first time since the bridge collapsed, they took a break to pay tribute to the six people killed.
"This ends with a tragedy of six. ... We are pretty confident that no one is left," Miami-Dade County Police Director Juan Perez said.
Under a bright Florida sky, workers stood with their heads bowed in silent prayer.
"We asked them to pause so we could pray over every victim," Perez said.
The prayers will continue. The questions are just beginning.