( 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military known this , the report said that his authorization to access secure facilities and information `` would have been revoked . '' CNN 's Evan Perez contributed to this report .
Report says employees at contractor noted behavior that raised concerns . The report by the Navy said had it known , the government would have yanked clearances . Alexis Aaron shot and killed 12 people last year before being killed by police .