Barnett, a quality manager with over 30 years at Boeing, had spoken out about safety concerns in the company's aircraft production.
He was in Charleston for legal interviews related to a case against Boeing and had given a formal deposition before his death.
Barnett's concerns included issues with quality control and safety at a Boeing production plant in South Carolina, particularly with the 787 Dreamliner jets.
Despite raising concerns to supervisors, Barnett felt his warnings were disregarded, leading to his transfer to another plant.
The circumstances of Barnett's death, reportedly a self-inflicted gunshot wound, add a tragic dimension to the ongoing controversy surrounding Boeing's safety practices.
Barnett's concerns, highlighted in articles by the BBC and New York Times in 2019, included potential safety compromises due to workers rushing to complete 787 Dreamliner jets.
Among Barnett's alarming findings were clusters of metal shavings near critical flight control systems and serious issues with the oxygen systems of the 787 Dreamliner, potentially jeopardizing emergency procedures.