I'll put the link here that I had earlier. It doesn't talk about betting (that I could see) - but, it does talk about the horrors that occurred and it's certainly reasonable to see that people would bet on anything, they always have and they still do!
Fort Smith was famous for all the hangings that happened there, it was the court for the huge territories to the west where the outlaws hid.
http://www.geocities.com/trctl11/hanging.html
What changed in western society that public executions moved into privacy?
The advent of newsreels?
A fundamental change in western sensibilities?
Crowd/riot control fears?
Increased urbanization & sophistication of population, moving us away from dealing with unpleasantries?
Or could it have been that the advent of electric chairs and gas chambers forced executions indoors and we became accustomed to indoor executions?
And now we've gone to injection - taking away even more of the glamour
