They benefited hugely from this and I have to this day not seen a public commitment to change things to make sure this does not happen. Even if Amazon was unaware of what they were doing, the fact that afterwards they mostly just papered over it and went on with their lives lends it a tacit approval ("don't get caught again"). If you don't see how this makes them evil, I think we just will never agree on it :)
The firm kept slaves (took passports, no pay, etc) to do the work in the warehouses that were guarded. Free labour is very cheap, that would be how they benefited.
