You should realize that your head is like a bowling ball sitting on top of your neck, and it takes muscular effort to support it. Everyone has their own distinctive postural way of doing it, and here we are seeing the same neuro-muscular signature. That's the same guy. In both images, he is holding his head the same way.
Here is a guy who does it by lifting his chin.
You can see how different that is. Here are two that are polar opposite to each other.
But, these two are exactly the same:
That is the same head/neck configuration.
Ruby held his head differently.
There is just no doubt that this guy in the center was FBI Agent James Bookhout.
And I'll remind you that I wrote to his son, and I invited him, I urged him, to deny that that is his father, but I got no response from him. Why? It's because he couldn't deny it.