Bridges don't usually crumble into dust. So when a pedestrian walkway at Florida International University collapsed Thursday, killing six people and crushing eight cars, people were rightly horrified and confused. Workers had installed the bridge overnight only five days before the disaster. FIU even blasted out videos and news releases celebrating the project's completion — especially since a student had been killed while trying to cross busy SW Eighth Street in 2017.

Instead, a good idea has turned into a nightmare for the university and the families of six dead victims. Authorities are still sifting through the rubble to figure out what happened. They'll have to answer the following five questions before any investigation is finished:

1. Why were cars allowed to drive under the bridge while it was being stress-tested?

It's now clear that the pedestrian bridge at Florida International University collapsed and killed six people after engineers put it through some kind of "stress testing" earlier in the day. According to Sen. Marco Rubio, the bridge's internal support cables were being "tightened" just as the bridge crumbled onto traffic below, crushing eight cars under 950 tons of concrete and steel.

But no one has yet explained why cars were allowed to drive freely under an incomplete bridge while workers were testing to see if it might fall apart. Now, some local officials are demanding answers.

Miami-Dade County Commissioner Xavier Suarez, who has a background in civil engineering, said he was flabbergasted that SW Eighth Street was not shut down to traffic before or during any stress tests or cable adjustments on the unfinished project.

"Never in my life have I heard of that," Suarez said. "That makes no sense. That makes no sense."

2. Was the bridge installed too quickly, and why were the temporary support beams removed?

FIU tweeted out video of the bridge "swinging" into place only five days ago — FIU press materials noted the construction method was designed to allow the structure to be assembled as quickly as possible.

"This technique reduced potential risks to workers, commuters and pedestrians and prevented traffic tie-ups in the area," the university wrote.

Just three days ago, a firm called BDI celebrated online that the company was "thrilled to have performed structural monitoring" on the project. After the collapse, BDI deleted its tweet.

3. Did political contributions help Munilla Construction Management get this job?

To Miami-Dade County insiders, it was no shock when Munilla Construction Management (MCM) beat out three other competitors to win a $14.2 million bid to build a high-tech pedestrian bridge at Florida International University. That's because Munilla is not only one of the biggest contractors in South Florida but also one of the most politically connected thanks to years of shelling out hundreds of thousands of dollars to campaigns.

Investigators are still sifting through the wreckage from yesterday's deadly bridge collapse that killed six, and there's no clear answer yet what went wrong.

But questions are bound to be raised about Munilla's deep ties to local politicians, including U.S. Rep. Mario Diaz-Balart and Miami-Dade County Mayor Carlos Gimenez — especially because the firm has never been shy about turning its political generosity into favorable decision-making.

Just take a look at the last election cycle, when Munilla executives and entities dropped an eye-opening $25,000 into local campaign coffers, according to a Miami Herald analysis at the time. In fact, the firm was the only company the Herald found that had given generously to all six county commissioners running for reelection.

Not coincidentally, the county commission has steadfastly voted to back Munilla's ongoing legal protest that has held up an $800 million federal project to build a new I-395 bridge downtown.

The Munilla firm is owned by a large family including Pedro, Jorge, Juan, Pedro Jr., Raul, Fernando, and others. And as their business grew, so did their reputation as rainmakers for local politicos.

4. Was the failure due to an engineering or construction error?

All 950 tons of the main span of the $14.2 million, 174-foot bridge crashed onto the road around 1:30 this afternoon. The structure, which spans all six lanes of SW Eighth Street at 109th Avenue in West Miami-Dade, had been installed only five days ago. Last Saturday, FIU, governmental officials, and construction firms blasted out celebratory images of the bridge being installed using a technique called "accelerated bridge construction," or "ABC," which is designed to build the structures as fast as possible. Instead, the FIU-Sweetwater UniversityCity Bridge, which was not scheduled to open to foot traffic until 2019, collapsed onto eight cars waiting at a red light.

Earlier today, Miami-Dade County Mayor Carlos Gimenez (who is in Hong Kong researching public transportation projects) said the bridge had undergone a "stress test" this morning just before the collapse. Some engineers have speculated the test might have triggered the disaster, but the accident's official cause has not yet been determined.

5. Did government officials properly vet these construction and engineering companies?

Two of the biggest firms that built the Florida International University pedestrian bridge that collapsed today have recently been accused of unsafe practices. In one of those cases, another bridge project toppled onto workers.

Police and fire-rescue personnel are still on the scene at FIU, where multiple people died in the rubble of the 950-ton bridge, which crumbled onto SW Eighth Street traffic. Investigators will likely spend weeks sorting out what went wrong on the project, which was described by the school as a state-of-the-art bridge made with new, high-tech materials.

Munilla Construction Management, a South Florida firm, beat out three other finalists to win the bid to build FIU's bridge, which was part of a $14.2 million project funded by the U.S. Department of Transportation. The firm partnered with Figg Bridge Group, which is headquartered in Tallahassee and has worked on iconic projects such as the Sunshine Skyway Bridge in Tampa.

Munilla was accused in Miami-Dade Civil Court March 5 of severely injuring a TSA employee at Fort Lauderdale-Hollywood International Airport because of shoddy work. According to the lawsuit, Munilla — which has a major contract to expand the airport — built a "makeshift bridge" through an area where airport workers must walk to reach restrooms.

Jose Perez, a TSA worker, was walking on the bridge October 20, 2016, when it "broke under [his] weight" and sent him falling to the ground.

"They built this makeshift bridge in the area where all the employees work, and it was poorly done. He fell and hurt himself really badly," says Tesha Allison, a lawyer representing Perez. "He had multiple broken bones and damage to his spine... They did shoddy work."

Update: A spokesperson for Munilla says that the "makeshift bridge" mentioned in the lawsuit was actually just a plywood pathway and that the case is a simple slip-and-fall at a construction site. Here's the statement from the company:

"In regard to the incident at Fort Lauderdale Hollywood International Airport that is being reported on, we want to make it clear that there is no bridge, or temporary bridge, at this project. This was simply a trip and fall accident that occurred on the ground floor involving a piece of plywood that was covering a sidewalk under construction. To report that this is in any way similar to the tragic accident involving the FIU pedestrian bridge is simply wrong and irresponsible."
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The FIU project isn't the first major bridge built by Figg to collapse in recent years. A Figg-assembled span in Virginia fell apart in June 2012 while under construction. Workers were installing a 90-ton concrete portion of the South Norfolk Jordan Bridge when it dropped 40 feet onto railroad tracks below, according to the Virginian-Pilot.

Four workers suffered minor injuries, but state regulators later said it was pure luck that no one was killed.