I dunno about Topsy, but Mary was hung because she'd killed someone and the owners were afraid she'd kill someone else. She'd stomped an assistant elephant keeper's head plumb flat after he'd caught an elephant hook in her ear. Normally she was a very gentle soul, I understand, and had been with the same circus for twenty years. It wasn't some sort of backwoodsy murder trial, but a decision to kill an animal. They didn't have rifles powerful enough to shoot her and the other option was to smash her between two locomotives.