The torturers were able to do this because they are psychopaths and see the “criminal” as less than human. Some psychopaths become serial killers, while others torture and kill “legally.”
I had a conversation with a Navy colleague at a previous job. He says that most soldiers fall into 2 categories: 1) some looking to make money, and this was the best option, and 2) legit psychopaths that want to be able to kill legally.
He said, you want those psychopaths on your side and that they are great soldiers