By international maritime law, any ship at sea is required to assist in search and rescue, if they can do so safely and there is a chance of saving lives. That

By international maritime law, any ship at sea is required to assist in search and rescue, if they can do so safely and there is a chance of saving lives. That doesn't mean everyone is required to send expensive assets for deep sea recovery of debris and remains, but for that time that there seemed like there was a chance, however remote, that the submersible might be bobbing on the surface with no way to open the hatch, there was a real legal obligation to search if possible.