Don,
I'm really sorry to her about your cat. I've experienced similar behavior before in a Russian Blue that we got from the humane society, but we always assumed it was the result of too much inbreeding. You mentioned that your cat had been feral, and from experience I've found that cats who have grown up in the wild can exhibit irremedial behavioral issues, including paranoia and aggression, sometimes the result of malnutrition, parasites or traumatizing incidents during their early life. Here's a link to an ASPCA site discussing cat behavior issues, including this except regarding redirected aggression. Given that there was a cat yowling outside the window this may be related:
Aggression in Cats | ASPCA
"Redirected aggression is probably the most dangerous type of cat aggression because the bites are uninhibited and the attacks can be frightening and damaging. Unfortunately, it’s also a very common type of feline aggression. Redirected aggression occurs when a cat is aggressively aroused and agitated by an animal or person he can’t get at (because there’s a window between them, for example). Unable to get to the trigger of his agitation, he turns and lashes out at someone—person, dog or cat—who is nearby or who approaches him. There can be considerable delay between the initial arousal and the redirected aggression, as long as hours. This is why cat parents sometimes describe this kind of aggression as unprovoked or “out of the blue.” They weren’t even aware of the initial trigger (for example, a cat outside who passed by 30 minutes before the attack). A redirected attack occurs only if an agitated cat is approached or there’s someone close by. The cat won’t go looking for someone to attack! It’s not a malicious or even intentional type of aggression. It’s almost like a reflex, done automatically without thought. This is why it’s never a good idea to break up a cat fight or approach an agitated cat showing defensive or offensive aggression postures."