Update On Bandit

I posted a question about my oldest cat Bandit who snapped and attacked his brother Smokey. Bandit is still locked up in his own room. We have been letting him out supervised to visit with the other cats. He seems fine for a few minutes and then the the two boys will start growling at each other. We break it up before anything happens, but when they do fight it's to the death. Is this just a territorial issue or is there something I'm missing. I haven't really got any feedback on what to do other than take him to the vet, which we did and the vet said he was perfectly healthy. The Feliway diffuser is making the other two cats lovey but doesn't seem to have an effect on Bandit at all. We have had it in for a few weeks now, I don't think it's fair to Bandit to have him locked up but we have no other choice. I've had some say to let them duke it out and things will work out on their own but we don't want vet bills to pay for if one or both of them get hurt fighting with each other. Please help, I want things to go back to the way they were before. Bandit is still not himself, he's still more aggressive than he was before and I can't get the two boys to get along like they did before. They have never been apart and they seemed inseparable before this happened. Nothing new has changed and none of the reasons people say he snapped seems to fit.

Thanks for all the replies. I did forget to mention that both boys are neutered, have been since they were six months old, and the female is spayed. We introduced the female over a year ago and Bandit made growling sounds and hissed at her to show her he was the top cat but got over it and all have been living in peace since. Unfortunately we don't live in an area that provides help for behavior issues among cats. The vet suggested finding a new home or putting him down if it becomes a huge issue and he's a danger to us as well. He's my big boy, I'm not giving him up to someone and I definitely don't want to put him down for an issue like this. I just don't get how he can be up on your lap with his brother one minute and then trying to kill him the next. He hasn't been the same since this happened. It doesn't seem to happen at certain times, when we let Bandit out the two boys sniff each other face to face and the back end too and seem fine, then the growling starts and we separate them again. I wrote in my previous post a few weeks ago that when we had Bandit in the carrier that he had moments where he would stop hissing, growling and spinning in circles and just stare off into space. I'm wondering if it's something mentally or if he's become chemically in-balanced somehow. The vet mentioned Prozac to calm him down enough to be around the other cats, but we can't afford medication. I love him so much and just want the Bandit I know back.