What we know about the Surfside condo collapse

When a condo building suddenly collapsed in the Miami Beach area earlier this summer, killing 98, it shocked the nation.

Rescuers worked for days at the Champlain Towers South in Surfside to try to find survivors in the rubble. But hope faded after all surviving victims were rescued and the mission shifted to recovery.

In the wake of the collapse, profound grief and questions about how a massive concrete structure could just fall to the ground lingered.

As federal investigators piece together evidence, a trail of documents indicated the 12-story, 136-unit oceanfront condo building had substantial concrete structural damage to its pool deck area and was overdue for repairs.

While federal authorities have not yet concluded the investigation to determine the cause of the fall, a number of experts and engineers believe prolonged structural damage, delayed repairs and environmental issues over four decades could have contributed to the building's deterioration.

Here is what we know:

'Independent spirit'

The Champlain Condominium Towers North and South were built in 1981 in Surfside, Fla. a neighborhood that sits just north of Miami.

"Surfside always had an independent spirit. The Surf Club was really the center of Surfside and it was built in 1930. The owners and the members of that club. wanted to have their own neighborhood and didn't want to be part of Miami Beach," Daniel Ciraldo, executive director of the Miami Design Preservation League, told ABC News.

During the 70's and 80's, Miami city leaders were looking to transition into a higher-end market, according to the New York Times at the time.

But at that time, a quarter of South Beach Miami was made up of mostly retired residents, many of whom protested the idea of rebuilding the city as many feared displacement.

"In 1973, a building moratorium was imposed partially due to a decaying Miami and concerns about the sewage system," Ciraldo said. To rectify this, the condominium developers fronted at least half of a $400,000 bill to fix the sewage issue and resume construction, according to a Miami Herald report from 1979.

The Champlain Towers were the first condominiums built once the moratorium was lifted.

Early signs of damage

Signs of structural damage to the Champlain Towers South's pool deck and garage ceiling were reported as early as 1996. Western Water Co., a local contractor, noted in a report the pool deck of the Champlain condo building and the ceiling of the underground parking garage beneath needed "concrete structural repair."

The work was later completed and certified to the city in November 1997, according to documents obtained by ABC News.

"The most common problems are weather intrusions. The way you combat that is with good quality solid weatherproofing and paint; and those repairs need to be identified when they happen and repaired in order to maintain the strength and integrity of the building," Peter Dyga, the president and CEO of Associated Builders & Contractors, Florida East Coast Chapter (a national construction industry trade association), told ABC News.

40-year recertification underway

After a Miami-area building collapse in 1974, county lawmakers enacted a mandatory inspection for commercial and residential buildings 40 years after they're constructed. The Champlain towers were in the process of recertification when part of the building came crashing down.

Morabito Consultants, a structural engineering firm, was hired by the condo association in 2018 to conduct the inspection and reported, among other things, concrete structural damage ​to concrete structural slabs on the pool deck due to failed waterproofing. They estimated repairs would cost more than $9 million, but those repairs were never completed.

Frank Morabito, a consultant and engineer from Morabito Consultants, declined to comment to ABC News.

'Very good shape'

Despite the structural engineering report and the detailed construction plan from Morabito, Rosendo "Ross" Prieto, the former Surfside building inspector, told residents at Champlain Tower South at a board meeting in November 2018 that their building was "in very good shape," according to records released by the city of Surfside.

"When things happen related to building construction, builders are generally the scapegoats and it may be the quality of the building," Dyga told ABC News. "On the other end of the problem is with a building. One that is most common that we see is failing to maintain. One of the most important things about building maintenance is weatherproofing," Dyga added.

In April, two months prior to the collapse, Champlain condo owners received an itemized bill from the board, a two-page letter obtained by ABC News shows.

The estimated repair costs was nearly $15 million, $6 million more than what Morabito assessed three years before. The owners were expected to begin making payments beginning July 1.

Following the collapse, Prieto, who was no longer Surfside's building inspector, was placed on a "leave of absence," according to a statement from the city of Doral, where he had been listed as interim building inspector but has since been removed.

He has not responded to ABC News' repeated requests for comment.

'The future'

In the wake of the collapse, Miami-Dade County inspected more than 500 buildings that were approaching the 40-year recertification deadline to identify any obvious structural concerns.

Buildings in Surfside that are more than 30 years and more than three stories high were notified to begin recertification. Surfside operates as its own city and has its own building department.

"The future is what is the capacity of a small town when we're talking about really large development projects?," Ciraldo said. "And the corollary of what is the ability of a volunteer condo association to be the permanent stewards of these properties," he continued.

In late July, a Florida judge ordered the families who suffered losses from the collapse to be compensated $150 million -- $50 million in insurance and nearly $100 million in proceeds upon the property sale.

At the conclusion of the federal agency National Institute of Standards and Technology (NIST) investigation, which could take several years according to NIST experts, Miami-Dade State Attorney Katherine Fernandez Rundle has pledged to bring the matter to a grand jury, which will gather evidence and hear testimony and could recommend criminal charges or needed reforms.