I've also lived in Greece (and was in Greece when Ben went missing) and this scenario makes perfect sense to me. Barkas was working on a piece of land adjacent to where Ben's grand parents were fixing up the house and Ben must have walked over to have a look and there was an accident in which Ben was killed, possibly because Barkas didn't see him and ran him over. Barkas feels guilty and covers up the accident out of shame. Harming a child, however accidental it was, is a huge stigma in Greece. Barkas died last month of cancer so now the witnesses are coming forward. It doesn't say a lot about Barkas' character that he covered this up but then there are many weak people in the world and I am sure his life was ruined with that decision, haunted by inner demons. How can it not be? The witnesses must be credible and the timing makes perfect sense so I presume the police are taking this seriously. My guess is that Barkas must have confessed to his friends or family and they waited till after his death to report it to police.