The only use of the proverbial 16-ton weight, that I know of, was the Salem witch trials where a man was sentenced to be "pressed" under a large slab. Given a sizable iron weight dropped from a fair height, it would be pretty darn quick (if that's the definition of humane they want to use). Pretty easy cleanup too, just hose the room down, and a fill a drum from the catch basin with the remains. ;-)