(NewsNation) — Improper repair work led to the deadly apartment building collapse in Davenport, Iowa, back in May, according to a new report released Thursday.

The preliminary investigation determined that repair work done three days before the partial collapse “severely compromised the western wall” after contractors removed layers of brick without adding proper supports. That weakened the wall and ultimately caused the disaster that killed three people.

“The temporary shoring that had been installed was grossly inadequate,” the report concluded. “Had a proper shoring and construction phasing plan been implemented during these repairs, the Building would not have partially collapsed.”

The investigation, which spans 113 pages, outlined several other contributing factors that led to the deadly collapse.

Read the full report below.

Among those, the report said engineers and masonry contractors who were responsible for the repairs “repeatedly misidentified the structural bearing wall as a nonstructural system.”

“As such, they underestimated the significance of the observable signs of distress in the wall, delayed necessary repair work, designed and installed a weaker replacement system, and removed significant portions of the wall without first installing adequate temporary shoring,” the report said.

Investigators said the construction documents from previous repair work did not provide “adequate details” for a contractor to implement the necessary repairs. That lack of documentation “limited” the City Inspectors’ ability to verify whether the repair work being done was “consistent with the engineer’s intent.”

Inadequate oversight also played a role, as there wasn’t a “qualified design professional” on-site during the repair work, the investigation found.

Earlier this week, the owner of the building filed a lawsuit blaming an engineering company for not warning the building was structurally unsound and that residents should be evacuated.

Residents have filed several lawsuits against the building owner, engineering company and city officials for negligence.

Documents released by the city showed that city officials and the building’s owner were warned for months that parts of the building were unstable.

The bodies of Branden Colvin Sr., Ryan Hitchcock and Daniel Prien were recovered from the site several days after the collapse.