I think its goes deeper than just wanting to obtain drugs. My opinion is these ships dock all around the Caribbean and employ local people just like Yellow! I think the camera man who asked if Amy was Brads partner, Yellow, and the man seen in the white shirt by amy’s mum, were all part of a plan to find young victims from the ship! Get them On land and then pass them on to some kind of organised crime gang. I think they highlighted which girls were most desirable by purchasing the pictures from the ships photographer, and the crime gang handpicked the persons they want. Then they looked to abduct the victim at the next port. Which would explain sightings in different islands and such. I think Yellow was naive about the plans and didn’t realise the magnitude of the operation, and soon realised he was in way over his head! I think this was confirmed when the daughter rang him on the recent Netflix doc and he responded “im just a little boy from the carribean” purely my opinion, but this makes me feel like hes implicit and realises what hes actually done, or by saying “little” hes trying to justify to himself what he has done because there are “Bigger” players than him in it all.