A famous movie director once said the film director is the last truely dictatorial post left. He was wrong. The captain of a vessel in international waters is.
Id also contend the spaceship is likely controllable remotely, and monitored in both location and status.
Maybe the private submarine captain trumps all
But the point about offshore regulations being hard to enforce is interesting.
Tldw: within a small number of miles of shore it’s police or federal (USA I guess it’s similar for other countries). After that it’s up to the ship. Cruise companies don’t want crime statistics so are unlikely to do anything about petty crime. There is death on high seas act but that only helps for a blatant murder. Jurisdiction is the flag which is likely to be panama or Bahamas. Your living areas can be searched any time and security can lock you up in your cabin. Cruises seem horrible to me and there are reports in the news of fights breaking out. But the worst thing for me is why be stuck on a ship that has less to do than I can do in my home city?
However, it seems to be a more or less open secret (from a friend of mine who works in the industry) that investigations won't be conducted as diligently as if the crime had happened on land.
Part of the reason for that is that it's difficult to secure evidence after several days or even weeks and the staff on board or the police in the next port often isn't qualified to do so.
Another contributing factor seems to be that cruise ship operators don't want any hassle or negative press and therefore push for investigations to be dealt with swiftly and silently.