Investigators are probing the cause of Wednesday's bridge failure in Minnesota.
It's a puzzle with twisted, mangled pieces, some jutting high into the air, others submerged under an eddying Mississippi River.
To piece together exactly what caused last week's bridge collapse here that killed at least five people, investigators are turning to a new 3-D laser camera technology and enhancement of surveillance videos.
Starting Monday, a computer simulator will model failure after failure, as investigators hope to find a wreck scenario similar to the scene that is bringing thousands of Minnesotans to the riverbanks to quietly reflect and mourn.
Early clues are leading some outside analysts to cast initial suspicions on recent construction activity on the bridge, wear-and-tear cracks in the metal, or both. And politicians across the nation, responding to sudden safety doubts among the public, are ordering inspections of thousands of bridges.
But federal investigators stressed that they may not have definitive answers, or new safety recommendations, for months.
"This is a long, very long, but thorough procedure," said Mark Rosenker, head of the National Transportation Safety Board (NTSB). "To try to give a bit of perspective on this, we just completed within about a year the final report on the Big Dig [ceiling panel collapse in a Boston tunnel]."
Mr. Rosenker reported significant progress mapping the wreckage, an important step given the river currents and recovery operations altering the scene.
With eight people still believed to be missing, officials said divers are inspecting each submerged vehicle, braving murky waters that supply only a foot of visibility and the glacier-like creaks and moans of the destroyed bridge.
On a tour Saturday of the scene, President Bush lauded the bravery of those involved in rescue efforts: "We have an amazing country, where people's instinct, first instinct, is to help save life."