I'm kind of confused? As far as I can tell, we need to figure out who is unaccounted for some time during the day, and had access to romans during that time. But the romans move randomly, and the disciples move randomly, so if a disciple is unaccounted for at a particular time there's no way to know whether they met romans or not, because by being unaccounted for they were necessarily in a place that may or may not have had romans in it?