A bike sold without rc transfer and got accident .

My father sold his old bike in 2007 the bike was not name transferred and got accident on 2011. as per in rc book my father name added him in this case. the case is still running... my father did not know the buyer who rides the bike and meet accident. the opposite party claiming amount. i have many doubts. 1. who is responsible for this claim as per in rc book owner or who got bike without name transfer rider 2. the vehicles was first sold to my father know person, now he is not here don`t know his status. second my father know person sold that bike to auto consulting in Coimbatore. we had that duplicate sold receipt copy. The buyer who got bike in tirupur and got accident. old man was died we have proof 1. the duplicate copy of sold receipt by auto consultancy 2. the rider who meet the accident. we are following this case through an advocate but we have doubt given all evidence still processing this case to many years. please give any advocate good sugestion