Feral cats are almost impossible to domesticate. Their "attack" responses are on a hair trigger. A cat with such hair-trigger responses may be lying in your lap, purring one moment and the next moment explode into a windmill of teeth and claws.
The attack may be triggered by a movement in the cat's visual field (a plant waving in the breeze) or touching the cat's fur unexpectedly with your hand. Anything that startles the cat sets off an attack.
A friend tells me that she successfully used Bowen Technique therapy for a feral ferret. As best I can tell it looks like cat-acupressure.