The National Institute of Standards and Technology released its findings Monday, blaming the disaster on two critical structural failures that happened three weeks before the building came down.

“Cracks grew and loads redistributed in the pool deck over the next three weeks.”

The connections between concrete slabs and garage columns failed, triggering a slow-motion collapse that residents never saw coming. NIST experts called it a punching shear failure — where downward forces on a steel-reinforced slab crack and bend it around a supporting column, overwhelming the connection holding everything in place.

The investigation, which NIST described as extensive, pointed to construction quality as the root cause. The 2021 collapse remains one of the deadliest building failures in U.S. history.

Victims’ families reached a $997 million settlement in the aftermath.