What is 'fog of war' and what are war crimes?

Soldiers are trained to kill people so why is there an inquiry into what our special forces were doing in Afghanistan?

source https://www.smh.com.au/national/what-is-fog-of-war-and-what-are-war-crimes-20201111-p56di8.html?ref=rss&utm_medium=rss&utm_source=rss_feed