Why were they acquitted? I have no idea as I was too young at the time to be following trials, but it doesn't mean anything about my previous statement was incorrect.
People can be cruel, but the goal is not often cruelty. In this instance, the goal for the officers was most likely to regain a feeling of power in my best estimation - a "how dare you not do what I say" attitude and they used cruelty to get it.
Again, their motivation doesn't explain why they got off, however. I disagree with that decision wholeheartedly.