About cruise ships, isn’t the simplest answer often best? Some people get thrown overboard, or fall overboard (drunk, accident, suicide) into international waters and the boat just….sails away?
On the one hand: yes. As in everything, Occam's Razor is going to apply here and when a person disappears from a large ship, 99% of the time they're going to have gone overboard in some non-homicidal fashion. Cruise ships have incredible mass and take a very long time to slow and turn, so even when witnesses physically
see a person go overboard the chances are very high that the person will be dead (simply via hitting the water) or unrecoverable by the time any recovery procedures are initiated.
However, there's the other 1%: cruise ships are lawless islands until themselves, flagged in countries like the Bahamas or Liberia for tax purposes and lower labor costs. Operating under the nominal "jurisdiction" of these countries, not wanting any bad publicity from crimes and deaths, cruise lines have zero incentive to properly investigate any disappearances or other shady doings. (That doesn't extend only to disappearances, but even to property crimes, violent assaults and rapes, some of which are chronicled at
http://internationalcruisevictims.org/ alongside people who've died because they received subpar first aid or medical attention.) Cruise lines are very much internally incentivized to sweep anything bad that happens on one of their ships right under the rug, and they bring so much money and employment to the countries they flag in that those countries (which normally have very limited law enforcement capabilities compared to western countries in the first place) aren't exactly beating down their doors to solve the crimes that occur on their ships.
So while Occam tells us that most disappearances have gone overboard while drunk - and people like the Bradley family are seriously overcompensating and fantasizing the way many family members of suicides do - we can concede that the conditions promoting nonprosecuted criminal acts on cruise ships are ripe enough that some suspicious things that happen on cruise ships and have been waved off as accidental may have actually been the results of criminal acts. About 20 people go missing from cruise ships every year and countless more die of medical conditions. You can't tell me that there isn't the occasional guy among those thinking "hey, this seems like a great chance for me to get rid of Jim."
Also, cruise employees are supposed to act as first responders for medical incidents and crimes before the affected passengers can be transferred to land personnel. Said employees are often basically untrained in these things and may be making as little as $650 per month on the entry level. Cruises should pretty much always be taken with an assumption that it's at your own risk and you aren't guaranteed any real medical help or proper criminal law procedures should anything befall your person.
