was he foaming at the mouth?
edit: If he was foaming at the mouth then he may have rabies, and if he does then he will need to be put down, and you need to get shots.
If he was simply being aggressive, then there are a variety of things to do.
If he is young, then it should be much easier. Simply you have to show him your the boss(leader of the pack) Once you achieve this he wont mess with you and wont want to.
My dad is the leader of our 2 dogs and all he has to do when those 2 dogs get in a fight is yell briefly at them, and they will stop. because they dont wanna mess with the papa.
This approach is the best approach. IS simply esstablish that you are the leader, and make him not want to mess with you.
Now another good option to do is to neuter him, if you have not done so already. Unless you plan on him having puppies, then there isnt much reason to not do this. Doing this will decrease his aggression, and cause him to be less dominate(as he wont have those hormones rageing through his system.
UNLESS YOU HAVE DONE AT LEAST 1 OF THE ABOVE, DO NOT FEED HIM MEAT THAT WAY.
If you want to give him scraps, make sure to put it in his food bowl.
Shooting is not a good option no matter what.
If you still have troubles, you can always ask the vet, or go to a dog forum.
As i dont know what breed he is I cant give more specific details, but from your theory that it ate a cat, i assume is is a medium/large dog.
If he is the size mentioned above, then you should be able to fight back if neccesary. You can hit him about as hard as you would hit a 8-10 year old kid, if they attacked you.
All of this is from my semi limited expierance with dogs. As i have raised 2 from when they were young, and one from a pound, and the other a stray, and both are mutts,(and medium sized).
THE NUMBER 1 THING TO DO NO MATTER WHAT, IS TO NOT FEEL FEAR NEAR THE DOG. DO NOT FEAR IT. IT CAN SENSE IT. This is from expieriance with a neighborhood pitbull, (large) that my siblings and i used to play with. Sometimes it became rough, and seemed aggressive.