If its true that real pro hitmans are able to kill people so that there is no doubt that it was a suicide... i would think that these jobs are rather dangerous. I really dont see a reason to kill yourself in such a position. I mean you will always find a new job, you wont be responsible for your failures and so on.

And with a nail gun? What CEO knows how strong such thing is? Can he be sure that it goes through the bone? And im not sure if i would willing to try it since i would fear that its not enough to die having a nail in the brain.