John Barnett had worked for Boeing for 32 years, until his retirement in 2017.
In the days before his death, he had been giving evidence in a whistleblower lawsuit against the company.
Boeing said it was saddened to hear of Mr Barnett’s passing. The Charleston County coroner confirmed his death to the BBC on Monday.
It said the 62-year-old had died from a “self-inflicted” wound on 9 March and police were investigating.
It makes no sense for them to kill him, that draws wayyyy too much attention. More likely if they were involved, they blackmailed him and that caused him to kill himself, or another party that also wanted to keep him quiet killed him and they didn’t care if it looked like Boeing did it.