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MIAMI (CBSMiami) — Investigators with the National Transportation Safety Board (NTSB) are trying to find out what caused a pedestrian bridge to come tumbling down at Florida International University crushing the cars under it and killing 6 people.

“Our entire purpose for being here is to find out what happened so we can keep it from happening again,” said Chairman Robert Sumwalt.

Experts told CBS4’s Silva Harapetian they are confused because when building a massive project, like the bridge, there are so many redundancies and safety factors that are built within the codes and protocol that something like this isn’t supposed to happen.

Miami-Dade Police Director Juan Perez weighed in their separate investigation so far.

“We don’t know that. We’re going to have to get to the bottom of that so we’re gonna have to start from the beginning from contract all the way to the end to the incident happening,” said Perez.

A reporter asked if traffic should have been shut down. To that, Perez responded, “You’re asking me engineering questions. I cannot answer engineering questions but we will get to the bottom of that.”

NTSB investigators have met with state, local and federal officials and did a general walk-thru of the area but don’t have immediate access to the scene due to search and recovery efforts. They’ve brought a team of 15 people at the site.

“They have expertise in civil engineering, material science, human factors, survival factors, and we’ve brought in our specialist from the office of Transportation Disaster Assistance,” said Sumwalt.

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While Miami-Dade Police are conducting a homicide investigation, NTSB is an independent federal agency that is investigating the cause of the collapse.

“We are working with the local officials but we are conducting an independent investigation that is not in any way related to any possible criminal charges,” said Sumwalt.

Friday morning, they were looking for witnesses who saw the collapse and they were asking anyone who had pictures or video of the collapse to please contact them at witness@ntsb.gov.

Chopper4 was over the scene just before 9 a.m. and an NTSB investigator could be seen talking to Deputy Mayor Kemp. Investigators arrived first on the scene late Thursday evening.

There are conflicting reports about what may have caused the collapse. Senator Marco Rubio, in a tweet, said the cables that suspended the bridge had been loosened and “the engineering firm ordered that they be tightened. They were being tightened when it collapsed,” and attached a video of the bridge collapse.

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. https://t.co/9Uc9EUsDYY — Marco Rubio (@marcorubio) March 16, 2018

That had not been confirmed by Miami-Dade Police as of Friday morning.

“I don’t even know if there was a stress test…I can’t confirm that,” said Miami-Dade Police Director Juan Perez.

Deputy Mayor Maurice Kemp echoed Perez’s comment as well.

FIU President Mark Rosenberg did confirm on Thursday that there were tests conducted on the bridge.

“I have not spoken to Munilla Construction directly but I’m satisfied that the testing that was occurring was consistent with best practice,” said Rosenberg.

The pedestrian bridge was an FIU project which means the university and its contractors are responsible for reviewing plans, permits, and inspection.

Miami based family business Munilla Construction Management partnered with Figg Bridge Engineering and the secondary engineering firm Louis Berger Group.

“We followed all processes competitive bidding to phase process and independent engineering company that is fully certified by the state that was recommended to us by FDOT,” said Rosenberg.

Governor Rick Scott is pointing the finger back at the university saying the project was not an FDOT project and the state was a facilitator for the federal funding of the project.

“There will be an investigation to find out exactly what happened and why this happened and we will hold anybody accountable if anybody’s done anything wrong,” said Governor Scott.

The Florida Department of Transportation is distancing itself from the bridge construction. Meantime, the university is saying they followed all processes and procedures.

Senator Bill Nelson, the ranking member of the Senate Committee on Commerce, Science & Transportation Committee, asked the U.S. Dept. of Transportation to turn over all records related to the engineering, design, construction, safety, and inspection of the project.

“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 wrote in his letter to Transportation Secretary Elaine Chao. “There should have been adequate and appropriate oversight on the ground. If anyone dropped the ball and it contributed to this tragedy, then they should be held accountable.”

Nelson also requested documentation detailing DOT’s involvement in the construction of the pedestrian bridge, including the federal grant agreement itself, among other documents.

As for NTSB investigators getting full access, that will be once the search and recovery efforts are done. Sumwalt predicts that once investigators get full access, they will be there about 5 to 7 days.

There are also investigators with OSHA and the FBI’s Evidence Response Team at the site.

Click here for more on our bridge collapse coverage.