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.
I like that one because I absolutely don’t like it, but it’s hard not to like and think that it’s worth being a likable conspiracy theory.
And that’s the problem with conspiracy theories, you like to like them and then you can’t be sure.
It’s just like that sometimes.