CHARLESTON, S.C. (AP) -- A former Boeing manager who raised safety questions about the aircraft maker and was found dead after several days of depositions in South Carolina took his own life, police said Friday after concluding their investigation.

John Barnett, 62, of Louisiana, was found dead March 9, and police had said earlier that his injuries were self-inflicted.

Barnett was a longtime Boeing employee and worked as a quality-control manager before he retired in 2017. In the years after that, he shared his concerns with journalists.

Barnett said he saw discarded metal shavings near wiring for the flight controls that could have cut the wiring and caused a catastrophe. He also noted problems with up to a quarter of the oxygen systems on Boeing's 787 planes.

"Information and records reviewed during the investigation uncovered Mr. Barnett's longstanding mental health challenges, which had intensified in connection with ongoing legal proceedings related to his whistleblower case," police said in a statement.

Barnett was in Charleston answering questions for depositions for his whistleblower complaint, and a hearing on the matter was scheduled for June.

"John was deeply concerned about the safety of the aircraft and flying public, and had identified some serious defects that he felt were not adequately addressed," Barnett's brother, Rodney, said in a family statement shortly after his death. "He said that Boeing had a culture of concealment and was putting profits over safety."

Boeing said in a statement, "We are saddened by Mr. Barnett's passing, and our thoughts continue to be with his family and friends."

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EDITOR'S NOTE -- This story includes discussion of suicide. The national suicide and crisis lifeline is available by calling or texting 988. There is also an online chat at 988lifeline.org.