John Barnett worked for Boeing for more than 30 years before retiring 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.