A commenter, Quartermain, just sent this link from mackwhite.com. It's a picture perfect portrayal of a man utterly lacking in conscience (though White only uses the word "sociopath" once).
I'd heard it speculated that LBJ was a sociopath, and hadn't doubted it based on what I knew, but had never looked into it that closely myself.
I hadn't known before, for instance, that Johnson had tortured and killed both a dog and a mule in his youth.
I had heard that Johnson had had sex with various women while his wife was in the next room; but I'd never heard that he'd actually fondled them while his wife was in the same room.
And I hadn't known about the hired killer Mac Wallace LBJ had at his disposal.
LBJ's possible connection to the Kennedy assassination will never be proven, of course. But reading about all the other things LBJ did does make one more inclined to believe it was real.
Part of the case that White makes is simply for LBJ's uncouthness. A lack of refined manners is by itself not proof of sociopathy; in fact, it can sometimes just mean that someone is merely unpretentious and more "real." But many of LBJ's well documented personal habits, such as conducting meetings while sitting on the toilet with the door to his stall wide open, are indicative of his complete lack of inhibition and embarrassment.
Normally when I put up a "sociopath alert" I try to make the case myself. But I can't improve on what White has written.