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The massive job of removing bridge debris and smashed cars from the site of the collapsed Interstate 35W bridge will begin today, authorities said Sunday, but a final report on the cause of the disaster will take longer than expected -- up to a year and a half -- because of challenges posed by the wreckage and the Mississippi River.

The announcement came as Minnesota Department of Transportation officials said that they had hired a St. Paul contractor for the cleanup, expected to cost up to $15 million.

As thousands surveyed the bridge wreckage Sunday from the reopened Stone Arch Bridge, searchers reported finding no new victims to add to the list of five confirmed dead, and Minneapolis police arrested five people for crossing police lines to take photographs of the collapsed bridge and to collect souvenirs. "We need to send a message," Capt. Mike Martin said.

National Transportation Safety Board investigators have concluded that the collapse Wednesday probably did not begin on the bridge's south end and will begin focusing today on the north side, he said.

The federal investigation is being slowed by the danger the wreckage poses to emergency workers and investigators, said Mark Rosenker, chairman of the NTSB, during a news conference near the disaster site.

The 19 federal investigators assigned to the case are being extremely cautious in their work, he said.

"The collapsed bridge continues to get weaker and weaker the longer it sits there, because the integrity is gone," Rosenker said.

The NTSB has given MnDOT permission to begin removing cars, debris and the superstructure, which will be closely examined to find the exact point where the collapse began, Rosenker said. MnDOT has hired Carl Bolander & Sons Co., of St. Paul, for the cleanup.

"It's going to be a slow, tedious process," said Terry Zoller, MnDOT's project manager for the debris removal. "It's not just a matter of taking pieces out and throwing them on a barge.

"The first priority will be recovery of the dead."

The work could involve dozens of workers and as many as four cranes and two barges, said Mike Koob of Wiss, Janney, Elstner, an Illinois-based forensics firm that is investigating the collapse for MnDOT.

"This is still a recovery effort ... and it will be focused on finding those who are missing," said Bob McFarlin, assistant to MnDOT Commissioner Carol Molnau.

The investigation

NTSB investigators will use a sophisticated computer program, updated by a former University of Minnesota student, to try to figure out how the bridge failed, Rosenker said.

The agency has collected an extraordinary amount of data for its investigation, including weather records dating at least 40 years, as well as preliminary information from the construction company on the materials and equipment that were on the bridge at the time of the collapse.

Photos at the time show a sand pile, a tanker truck and a concrete mixer on the bridge.

Rosenker said the weather data could prove significant because it would indicate possible patterns of the bridge's expansion and contraction history. All of the information, including weights, weather data and construction history, will be run through the model.

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