The stolen things were certainly valuable because they were ready to wait a long time for them. Jame was the leader, because be knew where the stolen things were and would not give the others any until it was safe. Jane had probably followed Jame and Tony from London. Perhaps he had helped them to steal the things, whatever they were. Then Jame, Tony and Josef probably argued with Jame and Josef killed him.
'I will see you in Athens, then' Mark said. Be careful.
'Stop worrying about me. I will be all right, I said as I left to go back to the hotel.