I think someone was thinking along these lines early when they spoke about cars not always being used by the registered keeper.
A Zafira isn't a car I'm overly familiar with. From my research however, I've noticed its a common choice for a Motability scheme car? I know, generally cars are new on this scheme but I think you can also purchase used cars. I remember reports of someone living in the house in Wilton close being in a mobility scooter. Is it possible they have maybe purchased this car on this scheme on behalf of a son/daughter/grandchild? Not a legit way of doing this but has been known to happen? This could explain why they are keen to trace other owners as they may need further evidence that a suspect was using this car if it isn't in their name? Maybe hoping that someone will call in with a tip? Also, I know it was said not to be local but that could just mean that they weren't a resident?
Suspect uses car for something untoward then dumps it back at friendly relative who kindly took it out in their name so as to distance themself?
Sorry if this is a rambling. My brain seems to go at 100mph when it should be sleeping!!