Independent of all other responses, I want to say this:

You did what you thought was right, OP, and it probably was. Holding back and calling the police without interrupting what was going on could have led to...well, it's tough to even imagine it. Don't tear yourself down over what happened; instead, let the pain strengthen your resolve to see justice done.

In the future, I would recommend (and this is horrendous, but it's the best I've got) recording the audio you mentioned in your original post if it was loud enough to wake you. The recording should be enough to initiate some kind of action on the part of the police, unless they're horrendously inept.

https://www.brickunderground.com/liv...s_being_abused

Also, read this if you like. It's all so...delicate.