That is really disturbing.
How hard would it of been to simply walk next door & explain the situation to the neighbor.
I'm sure he would of kept his cats indoor or put a collar on them with a bell.

Thats a BIG pet peeve of mine, people that do whatever they do (kill, call animal control, poison, steal etc...) to pets before even speaking to the owners.
A simple conversation could prevent a lot of time & trouble on everyones part.