Certain images will be indelibly linked to the Interstate 35W bridge disaster: Mangled green steel beams, giant concrete slabs that seem to float on the Mississippi River, a school bus frozen on a downward plane. Even as the search for those believed killed in the collapse continues, historians are thinking about how they should document the carnage.

Those who have chronicled other major tragedies say it's important to move quickly to secure artifacts, photographs and witness accounts that will convey the magnitude of the collapse years from now. Waiting too long, they say, can cause key items to be lost forever.

Minnesota Historical Society officials are discussing how to do that while being sensitive to the recovery and the investigation.

"We certainly don't want to be ghoulish or in any way disrespectful of the people who suffered in this tragedy," said Jennifer Jones, head of the society's collections department. But, she added, "This is indisputably an important event in Minnesota history and in American history, in fact."

As they gather media clippings, digital images and other written material related to the bridge, members of her team are compiling a list of iconic objects they want preserved.

They hope to obtain at least the emergency door from the bus that carried 52 children, the brass bridge ID plate attached when construction was completed in 1967, one of the beam-tying gusset plates that became an early focus of investigators, and a 35W road sign that came crashing down when the bridge did.

"It's difficult just because of the scale of the thing. What do you collect?" said Matt Anderson, a curator at the historical society. "You want objects that do speak and tell something."

State Department of Transportation officials are pressing to build a new bridge to ease congestion caused by the collapse by the end of 2008, but their plans may be delayed.

At the first official airing for the department's preliminary design for the new bridge on Tuesday, some members of a Minneapolis City Council committee complained that the proposed bridge would be an inadequate memorial to the collapse and wouldn't accommodate a future light rail line.

State legislators will get their first chance to weigh in Wednesday, at a joint House-Senate hearing where transportation officials are likely to be peppered with questions and complaints.

Divers and other rescue crews have recovered nine bodies since the Aug. 1 collapse, but stormy weather has delayed the search for four missing people believed killed.

Minnesota officials are far from the first to have to decide how to plan for future memorials soon after a disaster.

After the Sept. 11, 2001 terrorist attacks, curators for local, state and federal museums scoured the scenes, scrap yards and landfills for artifacts.

Columbia University history professor Kenneth T. Jackson, then the president of the New-York Historical Society, is still bothered that hundreds of thousands of pieces of paper that spewed from the World Trade Center towers were lost to history.

"I wished I had saved more rather than less," Jackson said.

David Shayt, a curator at the Smithsonian's National Museum of American History, vividly remembers his six trips to New York, the first coming three months after the attacks. He had a mental list of artifacts to pursue — including steel beams and other durable items patrons could touch.

He stumbled upon a three-drawer filing cabinet squashed to the size of a basketball and immediately recognized its value. "That instantly described a great deal in one small space," Shayt said.

In 2005, Shayt rushed to the Gulf Coast within days of Hurricane Katrina, not wanting to let too much time pass before beginning his search. His memorable find there was a kitchen wall clock lying in the dirt and stopped at 9:27 p.m. — around the time the powerful storm came ashore.

Collecting items is one matter; figuring out how and when to display them is another. The Smithsonian's National Museum of American History waited a year to open its Sept. 11 exhibit.

Minnesota History Society officials say they have no immediate plans for an exhibit.

"You've got to take into account how you are going to do this in a way that is going to be helpful to people and not simply increase their grief," said Jason Hall of the American Association of Museums. "Sometimes when you learn more about an emotionally difficult subject, it helps you get a grip on your emotions. It helps you pass through the grieving process."

Shayt said since the Sept. 11 attacks, many museums have been more willing to examine darker subject matter.

"The historical profession in general has matured and come to the realization that history is neutral," he said. "History and all of its warts and wrinkles and ups and downs is worthy of preservation."