Passage: Some Allied soldiers collected Japanese body parts. The incidence of this by American personnel occurred on "a scale large enough to concern the Allied military authorities throughout the conflict and was widely reported and commented on in the American and Japanese wartime press".The collection of Japanese body parts began quite early in the war, prompting a September 1942 order for disciplinary action against such souvenir taking. Harrison concludes that, since this was the first real opportunity to take such items (the Battle of Guadalcanal), "[c]learly, the collection of body parts on a scale large enough to concern the military authorities had started as soon as the first living or dead Japanese bodies were encountered".When Japanese remains were repatriated from the Mariana Islands after the war, roughly 60 percent were missing their skulls.In a 13 June 1944 memorandum, the US Army Judge Advocate General, (JAG) Major General Myron C. Cramer, asserted that "such atrocious and brutal policies", were both "repugnant to the sensibilities of all civilized people" and also violations of the  Geneva Convention for the Amelioration of the Condition of the Wounded and Sick in Armies in the Field, which stated that: "After each engagement, the occupant of the field of battle shall take measures to search for the wounded and dead, and to protect them against pillage and maltreatment." Cramer recommended the distribution to all commanders of a directive ordering them to prohibit the misuse of enemy body parts.These practices were in addition also in violation of the unwritten customary rules of land warfare and could lead to the death penalty. The US Navy JAG mirrored that opinion one week later, and also added that "the atrocious conduct of which some US personnel were guilty could lead to retaliation by the Japanese which would be justified under international law".

Question: Which group of people may retaliate due to how the bodies were treated?
Japanese