(CNN) -- Concerns about the "mental stability" of the Washington Navy Yard shooter were raised by his supervisors and others, but never reported to military officials as required, the Navy said on Tuesday.
Aaron Alexis, 34, killed 12 people and wounded several others in a rampage at the historic military facility last September before he was killed by police.
A Navy report placed much of the blame on Alexis' employer, a firm called The Experts Inc., a technology subcontractor of HP Enterprise Services.
The report said the former reservist previously had been "observed by several people," including supervisors at both companies, "to behave in a way that raised concerns about his mental stability and presented indicators that he may cause harm to others."
Had the military known this, the report said that his authorization to access secure facilities and information "would have been revoked."