Was the Killing of Osama bin Laden Legal?

This is a fascinating breakdown of the laws and treaties that govern wartime killing as applied to the recent operation that resulted in Osama bin Laden's death. It's a detailed and well-reasoned analysis, and an extremely informative read.
http://www.alternet.org/news/150911/was_the_killing_of_osama_bin_laden_legal/?page=1