Roger--

Maybe your cat needs therapy. Something along the line of guiding it to get in touch with its inner aggression and sense of territoriality. Maybe your cat SEEMS not to notice the evil intruder, but is actually seething about it inside and doesn't know how to express it. Maybe something traumatic happened early on in your cat's life in the litter box that is now blocking its expression.

I imagine there are many qualified professionals in nearby Berkeley who would be happy to work with your cat, perhaps even some who specialize in this particular type of problem.

Granted, therapy takes time. While your cat is getting in touch with its inner kitten, you might consider keeping it inside at night for a while and locking the cat door to keep out the cat burglar.