OP, you are the total asshole. He can leave his stuff where he likes in his property; you let your cat out and it died.

And you tried to make him the responsible when it was you, in reality.

I were him, I'd have stored the anti-freeze, but I would not feel OBLIGATED for it.

That said, if this tale is true, I have to acknowledge a grudging respect for how you ruined his sanity. If he'd been evil and killed the animal, I'd even consider it justified.

But as it is, you are in the wrong and ruining someone's life over your own fault.

Wonder if somebody ever points him to this thread, if I ever found out something like that had happened to me, that person's home or car might suffer an unfortunate accident.