I find the implied uncertainty puzzling: There is no doubt whatsoever that this strike, and the US drone war program in general, violate Protocol I, Articles 48 and 52(3) of the Geneva Conventions. Article 48:
In order to ensure respect for and protection of the civilian population and civilian objects, the Parties to the conflict shall at all times distinguish between the civilian population and combatants and between civilian objects and military objectives and accordingly shall direct their operations only against military objectives.
In case of doubt whether an object which is normally dedicated to civilian purposes, such as a place of worship, a house or other dwelling or a school, is being used to make an effective contribution to military action, it shall be presumed not to be so used.
This isn’t a complicated matter: It is the affirmative responsibility of combatants to know who and what they are attacking BEFORE they attack.
US drone operations don’t meet that obligation, either at the tactical end where it has been established beyond reasonable doubt that drones and their operators can’t distinguish between — for example — a group of civilian vehicles going to a wedding versus an armed, combatant al Qaeda convoy — or at the strategic end where US President Barack Obama sits in the White House and pretends that the drones and operators have that capability when he orders a “targeted killing.”
There is always plenty of doubt involved, and under the laws of war the benefit of that doubt goes to the civilians and non-combatants, not to the belligerents. QED, US drone operations are war crimes from top to bottom and beginning to end.