Welcome to Pet Talk.

You said that he has been attacking your other cat and that they have been together for 2 years without much problems. Is this something that he just started doing recently? If so, maybe a trip to the vet would be in order to make sure there isn't anything medically wrong with him.
The only thing at this time that I can suggest is, that when he starts his attacks, to grasp him firmly, but gently by the neck and tell him a very stern "NO", then put him in the bathroom or any spare room, by himself, for a time out. You have to be very consistent on doing this.
I wish you the best of luck with him cause this does not sound like fun to me.

BTW, what kind of cat is your Scooter?