SURFSIDE, Fla. — New documents show the Champlain Towers South condo building was badly damaged and needed millions of dollars in repairs to fix problems that continued to worsen in the months before last week's collapse of the 40-year-building.

In an April letter, the president of the Champlain Towers South condo association warned residents that damage to the structure's concrete support system was "accelerating" and "would begin to multiply exponentially" in coming years. The letter, written by president Jean Wodnicki, also offered a broad explanation of why residents were being asked to fund more than $15 million in repairs.

“When you can visually see the concrete spalling [cracking], that means that the rebar holding it together is rusting and deteriorating beneath the surface,” Wodnicki wrote. “Please note that the original scope of work in the 2018 report has expanded. The concrete deterioration is accelerating.”

The new revelation comes as Florida emergency personnel continued what they describe as a historic search-and-rescue effort, and as local officials accelerated their investigation into what caused much of the 12-story building to crumble.

At least one of the investigations will be undertaken by a grand jury, officials said Tuesday. “I plan to request that our Grand Jury look at what steps we can take to safeguard our residents without jeopardizing any scientific, public safety or potential criminal investigations,” Florida Attorney General Katherine Fernandez Rundle said in a statement.

Authorities also announced that another body had been identified, bringing the death count from the collapse to 12; 149 people remain unaccounted for.

State and federal officials are bracing for an agonizingly slow recovery effort, which could drag on for weeks or even months. Florida’s chief financial officer, Jimmy Patronis, who is also the state fire marshal, said nearly 370 rescue personnel, including all eight of the state’s Urban Search and Rescue Task Force teams, have been dispatched here.

With the Federal Emergency Management Agency and other federal agencies also involved, the White House announced Tuesday that President Biden and first lady Jill Biden will probably visit the site Thursday.

Florida Gov. Ron DeSantis (R) likened the continued search for survivors to “when somebody is missing in action in the military.”

“You are missing until you are found. We don’t stop the search,” DeSantis said at a Tuesday news conference. “That’s what’s happening. Those first responders are breaking their backs, trying to find anybody they can, and they’re going to continue to do that.”

As the rescue teams continue their work, officials have vowed to accelerate the investigations into why a big section of the building crumbled shortly after midnight Thursday.

Investigators are likely to closely scrutinize the damage to the Champlain Towers South building that the condominium association was in the process of trying to repair.

In her April 2021 letter, Wodnicki told residents of the 135-unit complex that $16.2 million in repairs were needed and that the association had about $707,000 on hand. Wodnicki said the board was asking residents to fund the remaining $15.5 million in costs with a special assessment.

Wodnicki told residents that the concrete work and other repairs were urgently needed.

“Extensive roof repairs” were required because “new problems have been identified,” Wodnicki wrote. The building was also “missing” a firewall between the lobby and the front driveway, she added.

The needed repairs were identified as part of the building’s efforts to receive the safety recertification required under Miami-Dade County’s housing codes. In 2018, at the start of the recertification process, the association hired a Palm Beach Gardens, Fla., engineering firm, Morabito Consultants, to examine the 12-story beachfront building.

In an October 2018 report, engineer Frank P. Morabito wrote that he had discovered “major structural damage” to a concrete slab below the pool deck in the section of the Champlain Towers South. The structural survey report also found that waterproofing below the pool deck and entrance drive had failed, allowing damaging leaks.

“Failure to replace the waterproofing in the near future will cause the extent of the concrete deterioration to expand exponentially,” Morabito wrote. He said a “major error” had been made in the construction of the building when waterproofing was laid on a flat slab rather than on a sloped surface to allow water to run off.

In a statement Saturday, his firm said that the damage he found “required repairs to ensure the safety of residents and the public” but that the repairs had not been started when the collapse occurred.

Despite the firm’s report, a Surfside building official told residents at the time that their property was in “very good shape,” according to the condominium association’s meeting minutes.

That official, Rosendo Prieto, has since left Surfside government and is now employed by a contractor working with the Doral, Fla., Building Department.

On Tuesday, Doral announced that the contractor, C.A.P. Government, has “assigned another employee to assist the city of Doral Building Department on a temporary basis.”

The contractor did not immediately respond to a request for comment or questions about whether Prieto’s absence was related to his tenure in Surfside.

Wodnicki’s letter from this spring suggested that the building’s condition continued to deteriorate even after the firm completed its initial inspection.

She added that the “largest phase” of the project involved repairs to the concrete and “waterproofing.”

Much of that work needed to occur underground and required contractors to “pull up almost the entire ground level of the lot,” Wodnicki wrote in the letter, which was first reported by USA Today and the Wall Street Journal.

“That means we have to put it all back at the end,” Wodnicki added. “This includes the pool deck, the entire entry drive and ground level parking, north side contractor parking and planters/landscaping.”

Wodnicki could not be reached for comment.

In recent days, residents have told The Washington Post and Miami-area media outlets that reports or leaks and flooding in the parking garage of Champlain Towers South stretched back decades.

One man who oversaw maintenance at the building from about 1995 to 2000 told CBS 4 Miami that saltwater would seep through the building’s foundation during particularly high tides.

Employees would use two large pumps to force it out, he said.

It is not clear whether those issues are directly related to the concrete damage that Wodnicki outlined in her letter. But Wodnicki told residents that the board was soliciting bids and had hoped to conclude the bidding process in early June.

As rescue operations continue at the collapsed site of Champlain Towers South, residents in the East building are juggling feelings of grief and isolation.

“This is a war zone,” said Marta Castro, a retiree who lives alone in a third-floor unit of Champlain Towers East, which was erected later than the other condo building, in the 1990s. She knew many of the residents who died or vanished in the sudden pancaking of the South building, she said.

In recent days, some of her relatives have urged her to leave the property, but she has decided to stay put. The road closures around the building have made it difficult to get in or out, Castro said, so many residents who have opted to stay feel almost marooned. Castro left her apartment Sunday to meet friends and get additional supplies; it took her more than an hour of circling around Champlain Towers to return home, she said.

“There are elderly people here who need to go for tests, go to the hospital. But it’s so hard to get in or out,” she said. “This shouldn’t be happening in America. This shouldn’t be happening in a developed country.”

Reis Thebault, Colby Itkowitz, Lateshia Beachum, Paulina Firozi, Jon Swaine, Beth Reinhard, Caroline Anders, Max Hauptman and María Luisa Paúl contributed to this report.