Crimes like this don't often happen on land. A 10-minute slow-motion slaughter captured by a cell phone camera shows a group of unarmed men at sea, possibly 15 of them, killed one by one by a semiautomatic weapon, after which the culprits pose for celebratory selfies. The shocking footage is then...

High Seas. High Stakes. High Crimes. There are few remaining frontiers on our planet. Perhaps the wildest, and least understood, are the world’s oceans: too big to police, and under no clear international authority, these immense regions of treacherous water play host to rampant criminality and...