Personally, I would have done the following, in order:
1. Report it to the local authorities.
2. Report it to my embassy in that country.
3. Report it to the cruise line.
4. Report it to the dive operator.
I don't see how the cruise line is responsible for tracking down and investigating a crime that didn't happen on their ship. I would like to believe the cruise line would have contacted the authorities and assisted in the investigation, but I wouldn't expect the cruise line to investigate it.
1. Report it to the local authorities.
2. Report it to my embassy in that country.
3. Report it to the cruise line.
4. Report it to the dive operator.
I don't see how the cruise line is responsible for tracking down and investigating a crime that didn't happen on their ship. I would like to believe the cruise line would have contacted the authorities and assisted in the investigation, but I wouldn't expect the cruise line to investigate it.