A deathbed confession can also be a way to solidify one's reputation by using the cultural belief in its veracity to double-down on the claim to increase general belief in it.
Let's say I had a bunch of secrets of exotic physics and decided to do a deathbed confession. Here's what I would say: "I've been working on antigravity and warp field physics for the last 50 years, in secret, with the US government." Then, instead of showing photos of a spaceship or a blurry alien, I would add: "And, here are the equations. Here is a diagram for how you build a device. Here is a working model. Here is exactly how you put everything together."
In other words, it shouldn't matter who I am, what my experience is, or what pretty (or ugly) picture I show. What I need to show is HOW to do it. Just saying something doesn't make it so. I need to give enough information for someone else to verify it and duplicate it. Otherwise, what's the point? To make a spectacle before I die?