MINNEAPOLIS -- Families continued a painful wait Thursday as officials in Minneapolis continued to search the Mississippi River for victims of an interstate bridge collapse. Meanwhile, officials began to plot investigations and inspections as they defended the presumed safety of the bridge.

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The collapse of the eight-lane Interstate 35W bridge during rush hour left at least four dead. On Thursday, at least 20 people were thought to be missing. Hennepin County Sheriff Rich Staneck said a dozen divers were in the water before 1 p.m. CDT.

He also said that on the bridge and in the water, officers were marking cars as they treated the area as a crime scene.

Dozens of cars are still submerged in the river, and inside them are many missing loved ones. Families have gathered at a Minneapolis Holiday Inn as they anticipate information.

At the Red Cross Family Center, Staneck explained why he was there.

"We came to reassure them that law enforcement officers are working very hard to locate their loved ones and give them some sense of comfort. We have a lot of people still unaccounted for and our job is to account for them," he said.

Gov. Tim Pawlenty called it a "day of horror, grief, tragedy and loss and burden," at a 4:15 CDT press conference Thursday.

However, he noted that it was also "a day of miracles within the horror," noting the fact that all the children on a school bus caught on the bridge escaped serious injury.

Pawlenty also praised the work done not only by first responders, but also passersby who risked their own safety to help those on the bridge.

"That reflects on Minnesota spirit and Minnesota goodness," he said.

Witnesses Speak

One driver whose car slid down the collapsing bridge said he was lucky his brakes were able to stop his car before going over the edge into the water. As he and other drivers got out of their vehicles and climbed up the incline, they rushed to get children off a nearby school bus.

He said the kids were "crying, screaming," as they were lifted out of the damaged bus. Click here to read more reactions from witnesses on the scene.

The first signs of roadside memorials were appearing Thursday afternoon in the area around the bridge. There were two small bouquets of flowers stuck into chain-link fence on a side road overlooking I-35W. One of the bouquets was from Mary Hovind, a St. Paul nurse.

She said she saw the bridge collapse on television Wednesday and drove to the scene in an effort to volunteer.

"How could I not go?" she asked. "I had to come down to see if I could help."

She found herself at the Red Cross center talking with some of the members of the road crew that was on the bridge when it came down. She said that all of the men were really distraught and were all waiting on word of one member of their crew who was missing that night -- and remained missing Thursday.

Hovind came back Thursday to place the flowers in the fence.

"I can't stop thinking about those guys," she said. "I'd never seen anything like it. It was something else."

'Structurally Deficient'

Minnesota Department of Transportation official Dan Dorgan said Thursday that while some inspections had found problems with the bridge and it was federally classified as "structurally deficient," it was also believed to be safe for service for a few more years. (Watch Dorgan talk about the bridge inspections.)

He said that the agency was looking to replace or redeck the bridge -- the most heavily used in the state -- sometime around 2020.

He said the bridge had been inspected every year starting in 1993, and that problems that had been noted included corrosion of bearings and signs of fatigue in the approach spans, not the main stretch over the water. Some cracks that were noticed were repaired. They were believed to be stable, however.

Tom Sorel, the Federal Highway Administrator, said cracks had been noticed on the bridge as early as the 1990s, but they "were not populating."

According to Sorel, the cracks were formed by the 1960s welding techniques, but they were monitored over the years and were not growing.

The most recent study of the bridge by an arm of the University of Minnesota confirmed that the bridge was "structurally deficient" and gave MnDOT two options: either use metal plates to stregthen and reinforce the bridge or conduct inspections and safety tests.

MnDOT chose the latter on the grounds that drilling and doing work on the bridge could potentially damage it further, Sorel said.

"We thought we had done what we could," said Sorel. "Obviously, something went wrong."

Bob McFarland, former chief of staff with MnDOT, said there were no cuts of budgets or inspectors and that de-icing was not a factor being investigated in the bridge's collapse.

He refused to speculate about causes.

The "structurally deficient" tag can be applied to about 8 percent of bridges in the state, Dorgan said. A bridge gets that rating when it scores below a 4 on a 1-9 scale in federal ratings. The bearing and corrosion problems led to the low ratings.

Tom Everett of the National Bridge Inventory Program, a federal agency, said that the term is "programmatic" and does not indicate a level of danger on a bridge, nor does it mean the bridge needs to be replaced.

A 2001 Minnesota Department of Transportation report looked at "fatigue cracking" on the bride and concluded:

"The bridge's deck truss has not experienced fatigue cracking, but it has many poor fatigue details on the main truss and floor truss system.

"The research helped determine that the fatigue cracking of the deck truss is not likely, which means that the bridge should not have any problems with fatigue cracking in the foreseeable future."

One Family Waits, Prays

Among the missing is Sherry Engebretsen, 59, a wife and mother of two. The Shoreview, Minn., woman is the director of marketing for Thrivant Financial Service. Her family said they are in agony, waiting for information.

"We called every hospital in sight and they said it's just a matter of time," said Engebretsen's 18-year-old daughter Jessica.

Engebretsen normally would not have even been on that bridge.

"She never drives that bridge. All of a sudden, yesterday, she took that way home and we don't know why," Jessica said.

Jessica, her sister and father are holding out hope.

"This is the hardest thing ever. It's really hard," she said, crying. "I honestly think I'm dreaming still."

Engebretsen's husband, Ronald, said he is relying on his faith to get the family through.

"I have great faith in the Lord Jesus Christ. I have to be strong for our family -- for Sherry's father and our two daughters," Ronald said.

He does believe his wife will be found.

"I'm holding on to the faith that we will find her," Ronald said. "In what capacity, I don't know."

Ronald said his wife was an intensely private person and never liked pictures. He was not comfortable providing her photograph to the media, but said he was considering it.

Bus Hero Shares Story

Jeremy Hernandez, a 20-year-old gym coordinator for a group of students from a summer youth camp that was on a school bus on the bridge, talked Thursday about his role in removing the children from the bus. (Watch Hernandez talk about his actions.)

He said that he was sleeping during the collapse, but was woken just as the bus started to fall. When it came to rest, he thought just the bus had been in an accident. When he heard students moaning and crying, he opened the back door of the bus, kicked out some coolers and began helping children off, despite continued shaking of the bridge.

He then handed them to others who came to the scene to take them off the bridge. He said the children were scared, asking for their parents and refusing to let go of adults helping them.

He said he had minor injuries, including to his hip, but was glad to be alive.

Investigation Calls For Reassembling Parts

Federal safety investigators plan to recover the components of the bridge and reassemble major parts of it to help determine the cause.

Mark Rosenker, chairman of the National Transportation Safety Board, said Thursday the investigation may take a year or more. Click here to read this full story.

At a 2 p.m. CDT news conference Thursday, Pawlenty said that he had ordered the state Department of Transportation to take three steps: hire and outside firm to conduct an investigation separate from the National Transportation Safety Board; hire and outside firm to review all state inspection processes; and perform emergency inspections on other bridges in the state.

The recovery effort continued Thursday afternoon, with Pawlenty noting efforts continued to slow the river down. He said vehicles were believed to be trapped under the fallen bridge and heavy equipment was being brought in to move parts of the debris.

Pawlenty said he and the NTSB would be asking some "tough questions" as the investigation continues.

"There was a failure in the bridge, but other things didn't go well or appropriately here," he said.

Government Officials React

"A bridge in America just shouldn't fall down," stated U.S. Senator Amy Klobuchar Thursday morning standing at a news conference attended by other local and federal officials.

Pawlenty said the bridge collapse "is a catastrophe of historic proportions for Minnesota."

President George W. Bush said that the federal government will help ensure that the collapsed bridge in Minneapolis "gets rebuilt as quickly as possible."

The Fire Department reported seven dead overnight, with 20 people missing as of early Thursday morning. A local fire chief said that death toll was expected to climb. But early Thursday morning, Minneapolis police Lt. Amelia Huffman said the number of confirmed fatalities was lowered to four. Police Chief Tim Dolan would not give a number of fatalities, saying that was up in the air. He did say that 20 to 30 people were considered missing.

"At this point I think there's still some unknowns," he said

Sheriff Richard Stanek also said he would not talk about the death toll.

"We know there are dozens of injuries as well, but it's too early to speculate and make a guess. It's unfair to the families," Stanek said.

There were at least 80 injured, according to Dr. John Hick, of the Hennepin County Medical Center.

"This is going to take a long time, this recovery," Dolan said. "We're going to have to do it slowly and safely."

Pawlenty told reporters that the bridge, built in 1967, had been inspected in both 2005 and 2006 and "no structural deficiencies were identified." The inspection team felt the bridge would not need to be replaced until 2020 or beyond. The governor confirmed that the construction taking place for the last few weeks was "minor" and "cosmetic," focusing on replacing lighting, concrete and guardrails and some work on joints.

The chief engineer in charge of the construction project told local reporters they were not doing any work on the structure of the bridge deck. Workers had been doing simple road repair on the pavement that started a month ago.

Sen. Norm Coleman, R-Minn., said there will be a full federal review of why the bridge collapsed. He spoke of a need for a "full forensic review." He said that hopefully it would not be the beginning of discoveries of other major structural flaws in the state's infrastructure.

"Clearly we have major issues with infrastructure," Coleman told KSTP TV News in Minneapolis. "Let's get focused on that."

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Coleman, along with other officials, said there was no indication from federal officials that the collapse was terrorism-related. The FBI was investigating, officials said.

"Clearly that angle also has to be checked out," Coleman said.

Emergency officials said the bridge collapse could be among the worst-ever disasters in Twin Cities history.

"For us, this is a big deal," Minneapolis Fire Chief Jim Clack said.

The Red Cross said it had established a phone number for the families of the victims: 612-871-7676.