Multiple structural issues led to the partial collapse of an apartment building in Davenport, Iowa, in May, that killed three people, according to report released Thursday.

Commissioned by the city and completed by Iowa engineering firms White Birch Group and SOCOTEC Engineering, the report identified improper support for an under-construction wall as the primary cause of the partial collapse of the six-story building.

Residents Branden Colvin, Ryan Hitchcock and Daniel Prien were killed in the Memorial Day weekend collapse, which destroyed dozens of apartment units.

The building was undergoing masonry repairs to its western wall before the collapse. The deficient support put in place during those repairs directly led to the collapse, investigators found.

"The temporary shoring that had been installed was grossly inadequate," investigators wrote. "Had a proper shoring and construction phasing plan been implemented during these repairs, the building would not have partially collapsed on May 28, 2023."

The investigators identified several "proximate" causes as well, including a misidentification of the improperly supported wall as nonstructural and several inadequacies related to oversight and documentation of ongoing building repairs.

Investigators noted repairs went on poorly supervised, in an "unsafe, incomplete, and improper manner."

"We engaged the services of the consultants who responded to the Surfside condominiums collapse in 2021, and we promised the public we would share their findings," Davenport Mayor Mike Matson said in a statement released with the report.

The building's owner, Andrew Wold, pleaded guilty in June to a civil violation for not maintaining safe conditions in his building. Wold was ordered to pay a $300 fine and $95 in court costs, according to a filing in Scott County Court.

Wold's attorneys confirmed in June he had "admitted to liability for a municipal infraction in civil court," adding their client felt the fine was "appropriate given the profoundly tragic collapse of the building."

In addition to the fine, Wold was ordered to "refrain from any violations of Davenport, Iowa (building) code provisions," CNN affiliate KWQC reported.

Wold is also among several parties facing at least two lawsuits from building residents. Both lawsuits allege negligence on the part of the owner and the city of Davenport, among others.

One lawsuit claims the building was not up to code and alleges complaints were known for some time, and it seeks an unspecified amount of money. Another lawsuit similarly claims Wold and the city knew about the dangers but failed to warn residents.

The city of Davenport previously declined to comment on pending litigation, citing the advice of its attorneys.