There seems to be little doubt that modern international law embodies the principle that, in addition to the individual responsibility of those who may actually perpetrate such crimes, criminal liability will also accrue to any political or military superior who orders, colludes in, condones, or fails to take steps to prevent their commission or repress end punish the actual offenders.
Green, Leslie C.
"War Crimes, Crimes against Humanity, and Command Responsibility,"
Naval War College Review: Vol. 50
, Article 4.
Available at: http://digital-commons.usnwc.edu/nwc-review/vol50/iss2/4