Edit: In all seriousness, I don’t think the situation presented in the aforementioned movie quote is implausible, though I’m inclined to doubt foul play here unless there’s specific evidence to that effect. Depositions can be extraordinarily stressful; compound that with the anxiety of being a whistleblower, and I can see how someone could snap. At the same time, I wouldn’t be surprised to find out that there was foul play.

If anything, the film quote is less realistic here insofar that it's not in context of a defense contractor with a large Rolodex.

Professionals tend to leave doubt rather than evidence. That said, even they make mistakes and therefore—to your point—it's unlikely it would be risked despite layers of intermediaries.

On the other hand, media cycles are short and PR is already in the trash can. This took place at the height of plausible deniability, and barring irrefutable evidence proving it wasn't foul play, it will be giving other potential whisleblowers pause.

The man's own attorney wrote:

"They found him in his truck dead from an ‘alleged’ self-inflicted gunshot."