Photo: The Canadian Press

Construction of the pedestrian bridge that collapsed and killed six people in the Miami area was behind schedule and millions over budget, in part because of a key change in the design and placement of a support tower.

Documents obtained by The Associated Press through a public-records request show that the Florida Department of Transportation in October 2016 advised Florida International University and its contractors to move one of the bridge's main support structures three metres north to the edge of a canal, widening the gap between the crossing's end supports and requiring some new structural design.

The span's 33-metre pylon was to be built atop a base at the span's northern end. It was designed for basic support and to contribute to the esthetics of the bridge, which was touted as an architectural marvel that would connect the rapidly growing university to the nearby community of Sweetwater. In their winning 2015 proposal, designers said the bridge provided "spectacular views" for both pedestrians using the bridge and drivers passing beneath it. They added that the tower could serve as a safety feature because it would have an "eagle-eyed location" for additional lighting and security cameras.

Videos of Thursday's collapse show that the concrete, prefabricated segment of the bridge started crumbling on the same end of the span where the tower redesign occurred, two days after an engineer on the project reported cracks in the same location. The segment that failed had been placed atop the pylon's footing, and the taller tower section was to be installed later.

U.S. Transportation Secretary Elaine Chao has ordered her department's inspector general to conduct an audit of the bridge, according to a news release Tuesday from the U.S. Department of Transportation. The agency awarded millions of dollars to the project.

It is still unclear if the design change contributed to the failure. But emails between the school, contractors, Sweetwater city officials and permitting agencies show a project that was behind schedule, which had officials worried that further delays could jeopardize federal funding.

When the bridge collapsed, the project was already running about $2.6 million over its $9.4 million initial budget, cost-tracking documents from February show. Originally scheduled to be completed in July, the finish date had been pushed back to January 2019.

Difficulties began in late 2016, when the Florida Department of Transportation emailed project officials saying they wanted more room to allow for future widening of the highway under the bridge, according to the documents.

After weeks of back and forth, it was decided to move the pylon to the north, sitting near the edge of the canal. According to documents, initial costs for the new design were $204,540, with another $402,723 for construction changes. The final cost was not divulged.

"The city attorney is advising us not to speak about anything to do with the bridge," said Sandra Antonio, a spokeswoman for the city of Sweetwater, which was working with FIU. The tower was to be located on the Sweetwater side.

Don Silver, a spokesman for Munilla Construction Management, or MCM, the Miami-based construction management firm that won the bridge contract, said the National Transportation Safety Board forbade engineers or contractors from talking about the project pending its investigation. MCM collaborated with Tallahassee-based FIGG Bridge Design on the bridge project, which also declined comment.