There are a lot of shady people involved in the military industry.

Why all, when one would do?

Boeing, a defense contractor, relies on killing people for financial gain.

No, he's saying that there's an army of lobbyists that see Boeing's financial health as necessary for their (clients') own. The lobbyists don't work for Boeing.

Imagine you had a highly lucrative SMB selling Microsoft services to some government/institutional customers, and some big court case threatened to cause MS serious harm, affecting your ability to sell those MS services. If you're a sociopath, you might want to shoot the star witness.

No, only one of the thousands needs to be willing to go that far. The power of stochastic terrorism...

Killing for financial gain is literally the business model of a large branch of Boeing.