How to find proof of purchase from someone that is now in prison?

So let me start off on how I got the iPad. My grandparents have a towing service. A man had his car towed from being abandoned on the interstate. Then my grandparents sign the paperwork and now everything in that car is theirs. This iPad is the air 2 model and it is iCloud locked. The problem is that I cant get ahold of the person who owned the iPad because he was arrested for a drug bust. Is there anyway I can get it unlocked???