I don’t understand why you’d say you want to rehome the dog instead of euthanizing him for literally killing your cat, being aggressive, untamable and incompatible with small living beings. If he attacks your cat, he will attack a kid if given the chance. Please don’t be irresponsible about this. If this happened to someone else’s pet, they’d report your dog, and he’d be taken, quarantined, have to pass a temperament test, which he’d fail, and then he’d be euthanized.
Rehoming him is a horrible idea and utterly irresponsible and downright criminal. Why would you want to set someone up to have this same thing happen to them or their kids or pets? Have some respect for your dead pet cat of 16 years and do the right thing: euthanize the beast you’ve known for 2 months who ripped him/her to shreds in what was a more torturous death than you can possibly imagine. You never loved your cat if you still love the animal who did this.
The dog was a “rescue” so who knows how many other cats he’s killed? You don’t know the dogs history but you know what he did to your cat. it’s stupid you’d consider carelessly perpetuating even more gruesome deaths because of your nonsensical love for the dog you barely know who viciously killed your lifelong pet. Do the right thing for your cat and for any unsuspecting victim you may have rehomed him to. Euthanize him. He’s not compatible with living a domesticated life.