One thing that a lot of people don't understand--and don't WANT to understand--is that sickos like this frequently get sexual gratification from this sort of thing, until the novelty wears off--at which point they start looking for victims further up the food chain.
The correlation is "power over" weaker beings, whether they be human or not.
Same as pedophiles.
It's a power/control issue.
They do literally 'get off' on it.