Even if every single attacking pirate's body were sent to Davey Jones' Locker, there's still the minor bit of evidence left floating up top ... the multiple vessels they arrived in, their gear, their DNA on that gear. Besides which, covering up the little deed could easily turn it into (at least in the minds of those seeking to resolve the puzzle) the appearance of murder.
Originally Posted by frenchman
Far better to report it and move on with their lives, hoping others will learn from the situation. If nothing else, others will learn of the continuing violence in that part of the shipping channels ... governments, military/security, owners of ships, and the general public. It's a bit like open-carry of firearms: people can begin to get comfortable with things once they begin to understand the truth of such things.