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.
[2 week later] Former lead detective found dead in in what investigators have ruled a suicide. He apparently hung himself after a fit of rage where his house appeared to have kicked in his own front door, tore the hard drive out of his security camera hub, punched himself in the face a number of times, then tied the rope to a bannister and strung himself up.