The Fifth Estate is not calling you because these guys are doing great and have never scammed anyone ever.
Plus, they clearly think you're currently involved whatever bad things they've been accused of and are dirt-digging, so say "I no longer own the domain and have no interest in the current business" and leave it at that. No good can come of attaching your name to this business.
It appears from my research (unconfirmed) that the current operators of Maplefinance.ca were connected to some people who operated a tax scheme in Canada. Do you have record of who the domain was sold to?
Since the guy obviously has no clue, I'd lay it out to him like this:
Imagine you sold a car to some random guy on AutoTrader, and then 10 years later it's used in a bank heist and a reporter keeps asking you for information on the bank robbery and the names of the thieves.