JIM LEHRER: That collapse of a bridge over the Mississippi River, special NewsHour correspondent Fred de Sam Lazaro begins our coverage.

FRED DE SAM LAZARO, NewsHour Correspondent: The rescue mission shifted to recovery this morning, 12 hours after the collapse. Cars clung to the broken concrete on what was left of the I-35 bridge, one of Minneapolis' major arteries crossing the Mississippi River.

Tim Dolan is the city's police chief.

CHIEF TIM DOLAN, Minneapolis Police Department: It is still a tremendously dangerous scene. We have several individuals at that scene that were not recovered. There are some unbelievable testimonials and stories involving a number of those people. And I can't get into the specifics because we have notifications and so forth to make.

FRED DE SAM LAZARO: The chief also gave new details about the difficult rescue efforts in the minutes and hours immediately following the collapse.

CHIEF TIM DOLAN: Some of the officers actually had to cross girders, swim part of the piece to get to that central area. It was a very, very difficult scene, very, very chaotic. And it was not just my officers; it was fire, ambulance personnel, medical personnel, so it was an all-out effort.

And when you see that scene, and you see the slabs that are hanging there, you realize just being near those slabs is dangerous, and they were crawling over them, so, like I say, tremendous courage.

FRED DE SAM LAZARO: It was the height of the evening rush hour, just after 6:00, when the 500-foot span of bridge broke into multiple parts and plunged into the river, taking at least 50 cars with it. The river is between four and 14 feet deep in that section.

COLLAPSE WITNESS: It was terrifying. It was just like something out of a movie. You stand there outside your window, and the bridge is buckling and the cars are sliding into the water.

FRED DE SAM LAZARO: This footage of the collapse was released by the Army Corps of Engineers this morning. Only four of the bridge's eight lanes were open due to construction, but the bumper-to-bumper gridlock gave drivers no room to escape.

COLLAPSE WITNESS: I think it fell four times, so we know we fell, I don't know, 40 feet -- we don't know how far we fell -- and then a car, we fell on a car. So we think the car might have been accelerating behind us, and my husband was trying to stop, stop, stop, because we didn't know what was happening.

FRED DE SAM LAZARO: After the collapse, many of the vehicles caught fire.

COLLAPSE WITNESS: All I could think of was, God, this was not the way I wanted to die.

COLLAPSE WITNESS: So me and some other people that had been climbing down the riverbank and stuff like that or getting people out of the water. There's one car that was sinking, and I know that -- nobody got out of that car. You know, me and some other guys -- you know, you want to go in, but the car's sinking. And it's tragic. It was awful.

FRED DE SAM LAZARO: This school bus carrying nearly 60 people, most of them children, barely made it across. Jeisy Aguiza was helping chaperone the children.

JEISY AGUIZA, Bus Passenger: I just felt the bus like go down, you know? Because I was about to go to sleep, so then I opened my eyes, and then I see dust.

FRED DE SAM LAZARO: Everyone inside the bus was able to escape, some with minor injuries.

COLLAPSE WITNESS: Me and about two or three other men were actually taking the kids off of the bridge and actually lifting them. They were screaming, crying. Dust just started coming up everywhere.

FRED DE SAM LAZARO: It was one of many heroic rescues.

MAYOR R.T. RYBACK, Minneapolis: Thank God this wasn't worse. And thank also the incredible team of people who responded to this disaster.

FRED DE SAM LAZARO: Most of the injured in the collapse were taken to or walked to nearby Hennepin County Medical Center. Families of the missing are gathering at a Holiday Inn to wait for news. This woman's brother is among the missing.

COLLAPSE WITNESS: Well, usually they're at my house all the time, everyday. It's just like they disappeared off the face of the Earth.

FRED DE SAM LAZARO: On a typical weekday, some 140,000 cars cross the bridge, which spanned nearly a third of the mile. At the time of the accident, several construction workers were resurfacing the 40-year-old structure. All but one have been accounted for.

It was held up by a single steel arch 64 feet above the river to avoid putting any piers in the water that would impede river navigation. The bridge was inspected as recently as last year: In 2005, the Department of Transportation listed it as, quote, "structurally deficient," with a rating of 50 out of 100, and possibly in need of replacement at a later time.

MARY PETERS, Secretary of Transportation: What that rating of 50 means is that the bridge should be repaired, should perhaps be considered for replacement at some point in the future. It was by no means an indication that this bridge was not safe.

Had that been the case, Mn/DOT, Governor Pawlenty would have shut this bridge down immediately. So none of those ratings indicated that there was any kind of danger here. It simply says we need to schedule this bridge for rehabilitation, and that was in the future program for Mn/DOT.

FRED DE SAM LAZARO: Governor Tim Pawlenty has ordered immediate inspections for all bridges in the state with similar designs. Federal funding will help that effort.

GOV. TIM PAWLENTY (R), Minnesota: If anybody at Mn/DOT were to come to me and say that we have a bridge that's imminently dangerous or is imminently in danger, obviously, it would be closed or other actions would be taken.

FRED DE SAM LAZARO: The NTSB chair, Mark Rosenker, said the investigation won't be easy.

MARK ROSENKER, Chair, NTSB: Each accident is very unique. Many are extremely complex. Some will take years. In this case, what we're hoping to be able to do is bring together as many of these parts, put them together, as I said, quite similarly to a jigsaw puzzle. And at that point, when we have all of the parts recovered, I believe it will be somewhere close to a year before we get our final report out.

FRED DE SAM LAZARO: Since the collapse, there's been a constant stream of people wanting to see the destruction for themselves.

COLLAPSE WITNESS: I drive on it every day to and from.

FRED DE SAM LAZARO: Some of the wreckage will be flown to Washington for analysis as the investigation moves forward.