Federal investigators said Tuesday that the 2021 collapse of the Surfside, Florida, condo building that killed dozens of people stemmed from a structural failure in the pool deck, not the tower itself.

The finding is in a study from the National Institute of Standards and Technology on the partial collapse of Champlain Towers South. Ninety-eight people were killed when the building fell early June 24, 2021. The agency said it used "large-scale structural testing and computer analyses" of video to determine that the collapse progressed from the pool deck through the tower. "It is more likely that the failure started in a pool deck slab-column connection," the agency said in a statement, adding that the findings also suggest "the building was in distress in the weeks before the collapse." Most residents were asleep in the 12-story beachfront condo building a few miles north of Miami when it fell at 1:22 a.m.

The points of distress were concentrated in a small area of the pool deck and street-level parking deck, the agency said, "which has been confirmed to have begun collapsing at least seven minutes before the tower."

Water was also seen leaking from the ceiling of the garage in an area that had many cracks and repairs over the years, according to the agency. The flow of water "dramatically increased" in the hours before the collapse, it added.After more than four years investigating the partial collapse, investigators said their work will most likely be completed by the end of 2025. The standards institute said it will produce a summary and six subject-focused technical reports.

Investigators have long thought the source of the partial collapse stemmed from the pool deck.

In 2023, investigators said poor construction of the deck in 1981 and decades of corrosion further weakened Champlain Towers South. In addition, renovations — including the addition of planters, palm trees and sand — placed a heavier load than the deck was designed to withstand, they said.

Three years before the collapse, an engineer assessed the building, finding that it suffered from faulty construction and structural damage, including corrosion beyond the pool deck. Documentation also showed that saltwater began seeping into the building's foundation years before the collapse.

Martin Langesfeld, whose sister, 26, and brother-in-law, 28, died in the collapse, responded to the standards institute's finding by noting that no one to date has been held accountable for the collapse and that he continues to seek "answers and justice."

“It has been over four years since 98 people were killed in their own homes, and NIST still has no answers," he said in a statement Tuesday. "There is no accountability, no criminal investigation, and yet a new building development is moving forward on the site. ... This is extremely insulting."

A luxury condominium is being built at the Champlain Towers site. Dubbed the Delmore, it's billed as "a collection of 37 mansions in the sky," with a starting price of $15 million. Dubai-based DAMAC International purchased the site at auction for $120 million.

The company said there will be amenities such as a see-through swimming pool, an indoor pool, an outdoor kitchen, a fitness center and a meditation garden.

The new condo is expected to be completed by 2029.