The first link between The Boy in The Striped Pajamas, Faces of the Enemy by Sam Keen and The Eichmann Trial in Retrospect by Abba Eben is the perceived awareness of "the enemy" or, as in The Boy in The Striped Pajamas' case, "the opposite."
The second link is evident when Sam Keen's Faces of The Enemy stresses the dehumanizing factor of "the enemy" such as it is a
"limbolike category, to which we may assign any threat about which we do not wish to think clearly"
and it compares with Adolf Eichmann's own recollections as:
"a life predicated on being obedient and taking orders is a very comfortable life indeed. Living in such a way reduces to a minimum one's need to think."
Both of these quotes make references to thinking - or, in fact, to not thinking - which allows a person's subconscious to deal with the horror of one's actions or to ignore events taking place. Keen goes on to stress that "It is not a person we kill, but an idea."
This reinforces the concept that the "real" enemy is unidentifiable. Bruno and Shmuel are supposed to be enemies but are in fact "friends for life." Abba Eben refers to the need to "distinguish between what is good and bad" and Bruno's understanding of this concept exists only in the realm of being an obedient child.
“What exactly was the difference? he wondered to himself. And who decided which people wore the striped pajamas and which people wore the uniforms?”
In the third instance, after Bruno's family are devastated on his disappearance, only after realising what probably happened to Bruno does his father begin to comprehend his actions. This links to what Keen says "From empathy comes a measure of compassion. To know in detail is to limit hate, perhaps even to abolish it." Although Bruno's father had been a part of the cruelty and evil, he never understood it until his own direct involvement in the tragedy.
"He who cannot remember the past is doomed to repeat it" (George Santayana) opens Abba Eben's essay The Eichmann trial in Retrospect. The closing lines of The Boy in The Striped Pajamas says "nothing like that could ever happen again. Not in this day and age." As much as mankind recognizes his flaws, so does he perpetuate his actions. So too with Faces of The Enemy - even in the title; there is a need to recognize the enemy, even if he comes from within!