MIAMI -- After the I-35 bridge in Minnesota came crashing down into the Mississippi River a decade ago, killing 13 people in rush-hour traffic, National Transportation Safety Board investigators raced to the scene to find much of their evidence underwater and being pulled apart by backhoes in a frantic search for victims.
In the painstaking months to come, they rebuilt portions of the bridge in a nearby park, using cranes and barges to move it downriver.
Ultimately, a grainy video image led them to the bridge's tragic point of failure, but not before they dug through years of inspection and maintenance records, constructed models, sampled the steel and concrete used to build the bridge and parsed 40-year-old design plans.
Two of the investigators on the case, Robert Accetta and Dan Walsh, are now applying that same methodical approach to unraveling the devastating collapse of the pedestrian bridge at Florida International University that killed six people last month.
Because the investigation remains open, Accetta, the lead investigator, declined to talk about specific details. But much of what he and Walsh learned during their 15-month investigation into what happened on a Minnesota summer day, along with other bridge accidents, will help them determine why 950 tons of concrete fell suddenly and seemingly without warning in a bridge touted as a feat in design, construction and safety.
"The evidence is probably the most important part," Accetta said in an interview with the Miami Herald. "Sometimes witnesses will report how they remember something ... but the evidence doesn't change."
When the Minnesota bridge collapsed, rush-hour traffic was bunching up on the bridge. Two southbound and two northbound lanes had been closed while workers were preparing to resurface the eight-lane bridge, which added tons of material to the bridge. Altogether, 111 vehicles were on the bridge, including a school bus carrying 62 students.
As the south span suddenly gave way, a malfunction eerily similar to the abrupt failure on the FIU span, a nearby motion-activated camera kicked on, showing the center span over the river drop nearly intact to the river below. In addition to the 13 killed, 145 people were injured.
As the search for victims continued over the next day, the local sheriff's office began pulling apart pieces of the bridge. They cut the concrete deck and a support beam with a backhoe and used blowtorches to pull apart steel trusses.
That left NTSB investigators with a mangled mess, not unlike the pile of debris strewn across Southwest Eighth Street when the FIU bridge, which was still under construction, failed.