Boeing whistleblower John Barnett, 62, was found dead in his truck in a hotel parking lot in South Carolina over the weekend.

Barnett blew the whistle on alleged safety problems at the aircraft manufacturing giant and had been giving evidence in a lawsuit against the company in recent days.

The Charleston City Police Department is investigating Barnett’s death, the office of Charleston County coroner Bobbi Jo O’Neal said.

Barnett’s former employer, Boeing, has responded to his death, saying: “We are saddened by Mr Barnett’s passing, and our thoughts are with his family and friends.”

Barnett worked with Boeing for more than three decades until his retirement in 2017.

He had voiced safety concerns at the airline’s manufacturing facilities and gave his initial testimony just days before he was found dead from what appeared to be a self-inflicted gunshot wound, the Charleston County coroner told BBC News.

In 2019, Barnett alleged that Boeing intentionally used defective parts in its planes and warned that passengers on its 787 Dreamliner might face a lack of oxygen if a sudden decompression occurred.

At that time, Boeing refuted Barnett’s assertions, stating that the company follows the strictest safety protocols.

On Saturday, US prosecutors initiated a criminal inquiry into an incident where a Boeing 737 MAX, flown by Alaska Airlines, experienced a mid-air fuselage rupture.

According to reports by the Wall Street Journal and The Washington Post, the Department of Justice (DOJ) has been conducting interviews with witnesses, including the flight crew, as part of its investigation into the event that took place on 5 January, where part of the aircraft’s body tore away during the flight.

Barnett had been staying at a hotel to provide a deposition in the whistleblower lawsuit against the company.

His attorney Brian Knowles told TMZ that he had doubts about the circumstances of his death.

“Today is a tragic day,” Mr Knowles wrote in an email to Corporate Crime Reporter. “John had been back and forth for quite some time getting prepared. The defence examined him for their allowed seven hours under the rules on Thursday.”

“Once you understand what’s happening inside of Boeing, you’ll see why we’re seeing these kinds of issues,” Barnett told ABC News in Australia in late January.