What are the laws in international waters?
On ships in international waters, the laws of the flag state apply. As for the sea in general, there ARE international conventions (such as the anti-whaling convention, the UNCLOS II convention, etc.) that limit what kinds of activities you can engage in on the high seas. But in your example, a murder that took place on a ship would be covered by the murder laws of the flag state. The trial would theoretically take place in a court of the flag state, although the captain could port and ask the authorities to help him deal with the crime if it wasn’t possible to return to the flag state.
