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John Barnett, a former Boeing quality control manager, was found dead over the weekend from what appeared to be a self-inflicted gunshot wound days after testifying about safety issues with the company’s aircraft production.

The 62-year-old had spent years speaking out against what he alleged were shoddy manufacturing practices at Boeing, where he worked for 30 years before he retired in 2017. Most recently, Barnett was in Charleston for legal interviews related to a lawsuit against the Arlington, Virginia-based company.

Here's what to know about Barnett and the safety concerns he's raised about Boeing.

Who was John Barnett?

Barnett spent decades working for Boeing, first at its plants in Everett, Washington, and, beginning in 2010, as a quality manager in North Charleston, South Carolina, NPR reported.

He first made international headlines in April 2019 when he and other former Boeing employees came forward to The New York Times to accuse the company of overlooking manufacturing issues in favor of making profits, putting passenger safety at risk.

The aircraft in question is a two-aisle plane that airlines widely use for international flights.

"As a quality manager at Boeing, you're the last line of defense before a defect makes it out to the flying public," Barnett told the news outlet at the time. "And I haven't seen a plane out of Charleston yet that I'd put my name on saying it's safe and airworthy."

What do we know about his death?

Authorities searched for Barnett at his hotel in South Carolina after he failed to show up Saturday for an ongoing deposition against the company.

Barnett, a Louisiana resident, was then found dead in a car outside a Holiday Inn from what the Charleston County Coroner’s Office ruled was suicide.  The Charleston City Police Department is investigating.

Barnett’s brother, Rodney Barnett, said in a family statement to the Associated Press on Tuesday that the years of speaking out against Boeing created stress for him and led to a decline in his mental health.

“He was suffering from PTSD and anxiety attacks as a result of being subjected to the hostile work environment at Boeing, which we believe led to his death,” the brother said.

In a statement to USA TODAY, Boeing said it was “saddened by Mr. Barnett’s passing, and our thoughts are with his family and friends."

What problems with Boeing's Dreamliner production have been uncovered?

Barnett became one of several whistleblowers who helped expose allegations of quality issues at Boeing in a 2019 New York Times investigation.

Barnett said he found discarded sharp metal shavings near electrical systems for the flight controls at Boeing’s factory in South Carolina, where the 787 jetliner is assembled that he said could have been “catastrophic” if the pieces pierced the wiring. After he raised the complaint to his superiors, Barnett claimed he was moved to another part of the plant.

A Boeing spokesman told the New York Times that safety issues are “immediately investigated and changes are made whenever necessary.”

Later that same year, Barnett told the BBC that he became aware of faulty installation of the aircraft's oxygen systems, which could deprive some breathing masks of oxygen in the event of an emergency. Boeing denied the claim.

Barnett filed a pending whistleblower complaint with the government, which had a hearing scheduled for June, the Associated Press reported.

“John was deeply concerned about the safety of the aircraft and flying public, and had identified some serious defects that he felt were not adequately addressed,” according to his brother Rodney's statement to the Associated Press. “He said that Boeing had a culture of concealment and was putting profits over safety.”

Boeing recently came under additional scrutiny this week after a six-week Federal Aviation Administration audit of Boeing and subcontractor Spirit AeroSystems found the company routinely failed to comply with quality control mandates.

The update came after a Boeing 737 Max 9 lost a door plug mid-flight during an Alaska Airlines flight in January. After the incident, the FAA grounded all Boeing 737 Max 9 planes with a door plug to conduct an investigation and inspect all the relevant aircrafts.

Late last month, Boeing was given 90 days to present a plan to “fix systemic quality-control issues."

If you or someone you know may be struggling with suicidal thoughts, you can call 988 any time day or night, or chat online. Crisis Text Line also provides free, 24/7, confidential support via text message to people in crisis when they dial 741741.

Contributing: Sarah Al-Arshani; Eve Chen; The Associated Press

Eric Lagatta covers breaking and trending news for USA TODAY. Reach him at [email protected]