VIDEO:
Surveillance Video of Collapse

Forensic officials who arrived on the scene of the I-35W bridge collapse in Minneapolis soon ruled out terrorism and seismic activity as causes. Nothing else is being ruled out as the cause of the Aug. 1 failure. "Anything is possible," says Mark V. Rosenker, chairman of the National Transportation Safety Board. "What we begin to do is rule things in."

Investigators are drawing information from a wealth of documents prepared over the past 10 years that detailed the aging steel truss bridge's physical condition and recommended possible fixes. But review of the structure's collapsed members had barely begun by Aug. 7 because search and recovery efforts required a delicate balancing act. Various agencies at all levels of government were taking turns combing the site for clues, damaged property and missing bodies. Divers and forensic engineers are working under intense river conditions, using a high-tech menu of investigative gear. They also will be aided by a finite element analysis program that modeled failure scenarios developed under a 2001 study by the University of Minnesota.

Getty Images Helicopter fitted with high-tech equipment gives investigators a better look at twisted wreckage of bridge trusses and debris.

NTSB is leading the federal investigation along with the Federal Highway Administration and the Federal Bureau of Investigation. Minn. Gov. Tim Pawlenty (R) ordered an independent state study and hired Northbrook, Ill.-based Will, Janney, Elstner Associates Inc. to lead that probe. The state also hired New York-based Parsons Brinckerhoff to examine its inspection procedures and expedite a sweep of the state's nearly 2,000 deficient bridges.

The bridge's long paper trail of inspection data, which goes back more than 10 years, and two independent research studies completed before the collapse will help shave down the overall probe by months, investigators say. "We are pleased to have some tools that we didn't have, for example, in the Big Dig," Boston's Central Artery/Tunnel epoxy failure last year, Rosenker says.

A 13-second surveillance video shows the southern end of the bridge shifting and falling. A domino effect ensued as the 1,907-ft-long bridge's main arch span, about 456 ft long, slapped into the Mississippi River. A spray momentarily cleared and the northern end then slipped backward off its pier.

The collapse killed at least five people and injured dozens more. It crushed a train underneath one of the northern spans, and took out a piece of a lock retaining wall on the other side.

One of the victims still presumed missing is Greg Jolstad, 45, an operating engineer employed by St, Michael, Minn.-based Progressive Contractors Inc., which was doing routine resurfacing work on the bridge. Jolstad, a member of operating engineers Local 49, was working inside a skid-steer loader when the structure fell. Several construction workers putting on a new 2-in. overlay on four lanes of the deck slab also were injured.

"They were just standing there doing their thing" when the span plunged more than 60 ft into the river, says Reed Leidle, senior project manager for Highway Technologies, a traffic-control subcontractor working near the bridge. Gary Babineau, 24, another construction worker, was passing across the bridge when it failed. He famously helped extricate some 60 children out of a school bus. The bridge was built between 1964 and 1967 and consisted of steel multibeam approach spans, concrete...