Bit off a strange question maybe but is there anyway to find out who owns a car without using cartell or something similar?

The reason i ask is last Friday someone parked a 2001 CLK 200 outside my parents house and he knocked at their door asking was it ok to leave the car outside as he couldn't get it started but would be back later to take it away,now its a public road so my father said no problem,then about 2 hours later he returned with keys and couldn't get into the car my father said he was 'clicking the key' for about 20 mins and the doors wouldn't open.

Now its a week later and the car is still sitting there and nobody has been back to it,so my parents been 71 are getting a little bit worried that maybe its stolen or something,the guy that knocked at their door had a strong English accent and my father said there wasn't anything suspicious about him but who knows.

The car isnt in the best of condition,it has NCT and the tax is just out and no insurance disc,would i have to contact the guards to find out its story or is there another way?

Thanks