Help! Resident cat is on a mission to kill newcomer

I'll try to make a long story short...about 2 weeks ago I trapped a homeless stray (possibly feral) had him neutered, shots, tested for FIV, FEL, etc., and brought him into my home- in my spare bedroom where I'm trying to socialize him. He's very hissy to me and I don't pick him up or pet him as he may bite. I got as far as he's eating in my presence and I'm petting him with a wand with fleece wound around it. He's hiding in my closet in the daytime to sleep. and I'm slowly trying to bring in the other 2 cats. One of my cats, Monty is pretty agressive, he's constantly by the bedroom door trying to paw and scratch etc. The other cat is blissfully nonchalant. I got a cage and put it by the closet so Monty could smell the new cat, that worked the first time. The second time Monty jumped on top of the cage and over it and right on top of the new cat and all h*ll broke loose! I broke up the fight with a squirt bottle but the other cat who was an innocent bystander got attacked by Monty pretty bad, I'm looking her over but I don't see any puncture marks, she does have thick fur. I looked at the newbie and he looks ok but more skittish today. Back to square one. I'm starting to wonder if I did the right thing bringing in another cat. But where can I take the new cat now? He's rather feral, no shelter will take him. But yet, There are so many people who have multiple cats..I know someone who has 11...another has 7...and yet they get along somehow.

Monty is neutered, 5 yrs old, he's had a traumatic life, was a feral kitten when we found him, then our resident matriach cat at the time terrorized him till she died 2 years ago, then he became the top cat. He also had 2 major surgeries for bladder stones. He's a nice cat otherwise, just very Alpha. The newbie seems rather passive, like the other cat we have. I think the two passive cats would get along well.

Anyone have any thoughts???

Sounds territorial to me...especially since they are both ex ferals. Have you tried the vanilla trick?

Perhaps you are trying to go too quickly with the introductions. If the new cat is semi-feral and is just barely tolerating you, why not give it more time to adjust to being in your home. 2 weeks is not a great deal of time. Our Simba hid behind our headboard for 4 full weeks before he would even come out if we were in the same room and he had no other cats to get accustomed to.

I personally would keep him isolated in the one room and work with him to get him more comfortable with the humans and then work slowly with the introductions to the other cats in the household. It can work I believe, but you will probably have to be VERY patient and not try to push it.