Based on what I have read and heard, this habbit of being nice to their hostages until the ransom is paid is largely a Somali phenomenon. Reports from other areas of heavy pirate activity, seem to indicate that pirates in these areas are far less kind to prisoners. I supose this could be at least partialy due to the fact that the organizations running vessals through those waters are less willing/able to pay ransoms for crews. In that case the crew would be, at best, witnesses and at worst and active impediment to the pirate operations.

SFC W