There are laws and there are outlaws.
Murder committed in the service of piracy is pretty much the definition of hostis humani generis (enemies of humanity).
From the Los Angeles Times:
Somali pirates shoot two couples, from California and Seattle, who had been on an around-the-world sailing trip when they were taken hostage off of Oman....MOREUpdate: I decided to repost a story from last year:
"Dealing with Pirates (and terrorists) Russian Style"