The mother of Aaron Alexis, the military contractor who killed 12 people at the Washington Navy Yard last month, told his bosses one month before the shootings that he had a history of paranoid episodes and most likely needed therapy. But Mr. Alexis’ managers at the Experts Inc., an information technology firm, decided to keep him on the job and did not require him to seek treatment, an internal company investigation has found.

The investigation by Hewlett-Packard, which oversaw the Experts’ subcontract at the navy yard and other military bases, concluded that the Experts mishandled Mr. Alexis and knew more about his mental problems than the company has disclosed, a person with knowledge of the inquiry said. As a result, Hewlett-Packard last week canceled its business relationship with the firm, saying it had lost confidence in its work.

“It is HP’s understanding that the Experts made their decision to return Mr. Alexis to duty without consulting a medical professional about his behavior, without determining whether he had seen a therapist as his mother suggested he might need to do, and without taking any other action to ensure that any mental health issues had been treated and resolved,” the person said. The person spoke on the condition of anonymity because he was not authorized to discuss the case publicly.

The Experts did not dispute most of the findings of the investigation, including that Mr. Alexis’ mother had made them aware of his history of paranoia. But in a statement, the Experts said that Hewlett-Packard was “fully aware” of problems Mr. Alexis was having in early August in Rhode Island, “and any claim to the contrary is baseless.” Over all, according to the statement, Hewlett-Packard supervisors consistently gave Mr. Alexis satisfactory or better ratings in the weeks before the shootings.