He says it's nothing to do with him, he's taken nothing to do with it in years, he's not been paying for it, didn't arrange the re-direction and doesn't know who did.
If the domain is in his name, address and email, he could theoretically take control over it, and stop the redirect. Alternatively and more safe from a legal stand point, would be to complain to the domain registrar and let the know that the whois info is inaccurate. They would then have to contact the person who's paying for the domain to update the whois (letting them know that you'll be contacting ICANN over this if the situation is not corrected swiftly might also help), and this might give you a chance to contact the real owner. Alternatively, this person never replies, and the domain will have to be taken down.
Things don't go as planned if this person who's been paying for the domain's registration chooses to purchase a whois privacy service instead of updating the info.
The domain itself must be hosted somewhere. Try to determine the host, and then see if they're willing to help out in some way (like maybe contacting the hosting account's owner an relaying your complaint).
You could also try to contact Google directly and explain the situation. It seems to me like something went wrong in their ranking algorithm. Still, as far as I know they're not the kind who will try to sort out individual problems, so, assuming they will take the time to really read your request, it could still take them months to act on it.
I'm not aware of a technical solution that can be applied on your side only, but I'm not the most knowledgeable person in this area. Personally I doubt there is one.
I'm not sure you have grounds for legal action, but that's always an option as well. Still takes time and money though.