Fallen bridge: 'Stress test' preceded collapse that killed 6

MIAMI (AP) — An innovative pedestrian bridge being built at Florida International University had been put to a "stress test" and its cables were being tightened when it collapsed over traffic, killing six people and sending 10 to a hospital, authorities said.

As state and federal investigators worked to determine how and why the five-day-old span failed on Thursday, one factor may have been the stress test that Miami-Dade Mayor Carlos Gimenez said crews were conducting on the span.

Two workers were on the 950-ton bridge when it pancaked on top of vehicles waiting at a stoplight.

U.S. Sen. Marco Rubio tweeted late Thursday that the cables that suspend the bridge had loosened and the engineering firm ordered that they be tightened. "They were being tightened when it collapsed," he said on Twitter.

First responders had been racing to find survivors in the rubble of the 175-foot span using high-tech listening devices, trained sniffing dogs and search cameras before turning the scene over to police.

"This has turned from a rescue to a recovery operation," Miami-Dade Police Det. Alvaro Zabaleta said.

The $14.2 million pedestrian bridge was supposed to open in 2019 as a safe way to cross the busy six-lane road between the university campus and the community of Sweetwater, where many students live.

At the accident scene, Florida Gov. Rick Scott said investigators will get to the bottom of "why this happened and what happened," and if anyone did anything wrong, "we will hold them accountable."

National Transportation Safety Board chairman Robert Sumwalt III said a team of specialists would begin its investigation today.