I amn reading a book entitled "Wings of Gold" by Gerald Astor, following is an account as told to him by Lieutenant Charles Brewer, about a kill stealing situation:
"Upon getting into range of another fighter, as I was about to fire, a friendly F6F slid in front of me and took out the target. Had I started firing, he would have flown right into my tracers. Lucky guy...."
So we know kill stealing (as we call it) happened during WW2, and it was a dangerous proposition for those that did it. In AH no such penalties occur for the offender.