homicidal cat

Are all the kitties spayed and neutered? If not, that would probably help a lot.
You could also try to use a spray bottle with water to redirect Smokey's behavior when you catch her in the act. To help Blackie's anxiety you can try Rescue Remedy. Consulting a vet about Smokey's behavior may also be in order. She seems very aggressive and although I'm not sure if it's the same for cats in dogs an over active thyroid and other medical problems can cause aggression. A friend of mine has a cat that acts out quite a bit and she has been helped by small doses of Xanax. It's possible that it could help Smokey too. I would try other things before trying such a heavy duty medication though.

Until the situation gets better I would not let Blackie out at all. Chances are that she'd leave for good if she's that stressed out over Smokey.

I'm sorry I couldn't be of more help. Hopefully someone else has better advice.

Good luck

Heres a piece of advice from someone with a lot of knowledge in this department gave me recently...

Anytime you let a cat outside, you destroy their general scent and when they come back in the house, they smell different and are treated by the other cats as an intruder. They can find a fresh kill in the grass and rub in it, or run up into some trouble and their stress pheromones go into overdrive and cause them to smell differently.You should keep all cats indoors always stop adding more cats into the home and use a neutral scent to help them calm down vanilla extract (pure) dabbed on their chins and the base of their tail should work.

If the attacks continue, the one being attacked could likely be sick and his signature scent is changing

I would keep them separated for now and treat it like a new cat introduction. I don't really know how to handle the indoor/outdoor part, because we have indoor only cats, so I really don't know how to adapt my advice to cats that are allowed outdoors.... but here's the advice I normally give, and hopefully you can figure out how to adapt it to your situation.

The basic idea is to use time, positive reinforcement, redirection, scent swapping, and create proper space to help "transform" the situation.

While doing the separation, rub Smokey and Blackie all over with a couple of hand towels or clean rags. Put a rag that smells like Blackie under Smokey's food dish, and one that smells like Smokey under Blackie's food dish. This helps them to begin associating each other with "good" things.

Given your cats go outside, I don't know if extra stimulation would help, but I normally recommend that you give the aggressive kitty extra play time to help 'absorb' the energy. At the end of the play session, put treats down on another rag that smells like Blackie. This will help Smokey associate Blackie with GOOD things. Of course, doing the same for Blackie won't hurt.

To help Blackie de-stress, and to help Smokey calm down, I also recommend the Feliway. This is a synthetic hormone that mimics the "friendly" markers in cats' cheeks. It comes as a spray or diffuser. If you get the spray, make sure you "refresh" it every 2- 3 days. I prefer the spray, because you can use it around the whole house rather than investing in a bunch of expensive plug-in diffusers.

As to the Flower Essences, it's the same ones used for humans - around here they're available in most health food stores. I'd get Rescue Remedy. You can put a few drops in the water, and dab a touch behind the ears, at the base of the tail, and under the chin.

Do you have much vertical space? Lots of places for Blackie to hide? After "reintroducing them" over a period of at least several weeks, this can also help diffuse introduction tension. Smokey can assert her dominance by going "up." Cat trees and condos, window seats - things like that can really help.

Consider purchasing some new toys that Smokey likes. When you bring Blackie out (or Smokey in Blackie's room) when you start the reintroduction process, doing a supervised intro, give Smokey a new toy, and play with her. Let her think having Blackie around is a total party. Get her favorite treats, put them on a rag that smells like Blackie. When she plays with the new toy in the presence of Blackie or eats the treats, tell Smokey WHAT a good girl she is. If she makes no aggressive moves to Blackie, tell her WHAT a good girl she is! Praise the heck out of her for doing nothing aggressive. ...but keep an empty can with coins in it, and if she goes for Blackie, rattle the heck out of it to stop the attack, and immediately remove her from the room. Tell her you want her to just ignore Blackie, and put her out of the room and leave it at that. Try again another day.

The point is that instead of emphasizing the negative (like squirting with a water bottle, which really should never be done, because of risk of ear infection, and all that really happens is kitty gets mad at you), emphasize the positive. When she gets to the point she's just looking at Blackie rather than growling or hissing or attacking, tell her WHAT a good girl she is! ... and maybe give them treats (always give Smokey hers first). Food goes a LONG way to helping kitties share space in a friendly way. ...and cats learn well through positive reinforcement.

The most important thing is to take it slow and give it as much time as it needs.

Is there a small room in your place that Blackie can be allowed in but not Smokey? It might give Blackie some sense of safety if there's some place she can go where Blackie can never get her.

I think there's lots of good advice to look into here. Please keep us posted!

Cheap large plastic storage containers with holes cut in the sides and stacked up in a "ladder" fashion or pyramid fashion work great for vertical space and hidey holes. ...just a thought.

...and chicken is a great treat!

...and yeah, cheese isn't a great treat, because most adult cats are actually lactose intolerant.

We, too, have a homicidal cat, and the only thing that works is to keep him separated from his victim(s). Haven't tried Feliway yet, but I don't think our two cats will ever be able to sit in the same room without the aggressive one going berserk.

Is simply keeping them separate a possibility? Ours are also indoor-outdoor, and they switch places every so many hours. When aggressor is outside, victim gets run of the house, and when victim is outside, aggressor gets run of the house. If it's cold out, and both are inside, aggressor stays shut in a room and victim gets run of the house. Or sometimes victim is shut in a room.

Keeping the cats separate is the most important thing in our house. The occasions when someone made a mistake and let the two cats meet were disastrous.

It sounds like you are doing something similar now...what isn't working? Maybe you could take Blackie out on her harness for a while each day, while Smokey is inside, so that she can enjoy the fresh air as well? That way, both cats would get some time inside and some time outside.

Don't give up yet. Although it can be a pain switching the cats around and keeping them separate, we've managed to bring some order and peace into the house. I hope you manage to do the same. Good luck!

My advice is get rid of the trouble cat.
Put him/her to sleep.

This isn't fair to your smaller cat to constantly get bullied like this.
Reading this pissed me off

Why would you allow this to happen.
You put a violet larger cat together with a calm submissive cat.

If it was me.. if I saw that cat attacking my smaller cat I'd grab it &
hurt it bad enough so it would get the message to leave the other cats
alone.

Now you have a smaller cat living in fear & being constantly abused

Yes this is very important! Blackie definitely needs a safe zone of his own that he can retreat to when Smokey goes after him.

The other thing too, is that when you do see Smokey going for Blackie you need to stop her behavior right away. The can of coins trick might help. You also need to tell her that "No! she is not to attack Blackie!"

Once in a while my younger cat Samson, decides that he wants to bully my older cat Rascal. Let me tell you, I don't let that happen. I break up any fighting between them immediately, verbally. Standing right over them and a couple of loud "Hey! Hey! Stop that!" works well, at least for my cats. Then I tell Samson that he is not to do. He gives me this "yeah yeah whatever look", but he does slink guiltily away.

I would also, as someone else recommended, get your cat's thyroid checked, just in case. It can't hurt that for sure.