More than four years after the deadly collapse of the Champlain Towers South condominium complex in Surfside, Florida, federal investigators are expected to announce their preliminary findings on Tuesday regarding the cause of the tragedy.

“It is more likely that the collapse initiated in the pool deck than the tower,” a slide deck prepared ahead of today’s National Construction Safety Team Advisory Committee meeting states.

Champlain Towers South was an oceanfront complex just north of the Miami Beach city line. The collapse of the structure killed 98 people in the middle of the night in June 2021.

Researchers from the National Institute of Standards and Technology have preliminarily concluded that the pool deck started to collapse more than seven minutes before the building fell to the ground, confirming what was suggested in earlier media reports.

The exact cause of the collapse has been under investigation in the years since the incident, but investigators have long focused part of their attention on the pool deck.

“At the time of the failure, the pool deck’s slab-column connections had critically low margins of safety,” the presentation notes. “The bulk of the critically low margins of safety was caused by design understrength and misplaced slab reinforcement.”

Officials noted in their presentation that issues with the pool deck existed from the time Champlain Towers South was built more than four decades ago.

“The structure had low resistance to progressive collapse, allowing the collapse of the pool deck to spread into and throughout the middle and east parts of the tower,” the slides added.

The federal probe into the collapse has been delayed several times. The final investigative report was previously expected to be completed in 2025, but that goal has since been pushed back another year.