Yes, it was a suicide, because his testimony wasn't part of anything related to whistleblowing, he was appealing a loss of the wrongful termination lawsuit against Boeing.
The idiots who never bothered to learn more than the man's name think "big company killed whistleblower" are showing just how little they understand things.
To recap, all the evidence from his whistleblowing was submitted to authorities 7 years ago. He had no bombshells to drop, no story that hadn't been told, just a lawsuit over how Boeing retaliated against him for Whistleblowing 7 years ago, forcing him to "retire".
A few days before he killed himself, he was on the stand in front of the appeals judges, and from all accounts, they did not seem like they were going to overturn his loss. He was then called back for another round of testimony, but was already dead by then.
Can you imagine a 7-year legal battle over being fired for having integrity? The stress this man must have felt?
Boeing killed John Barnett, but they didn't pull the trigger, he did. Don't cheapen that with lies about some sort of conspiracy. Just know that Boeing is one of dozens of companies who have worked for decades to weaken labor protections.