Why does Bruno lie about his friendship with Schmuel to Kotler?

The
original question had to be edited.  Bruno's lying to Kotler about Shmuel is motivated by fear.
 While Bruno's actions are in the name of resistance, he, himself, is not a resistance fighter.
 He only knows what he does as a reflection of his own good nature.  He is still a child in the
midst of overwhelming conditions of order and authority.  It is here in which Bruno lies to
Kotler.  Bruno is confronted with an agonizing moment.  If he stands up for Shmuel, there is an
immediate challenge to a brutal authority structure.  It is this structure that tormented Pavel,
a memory still fresh in Bruno's mind.  

Bruno does not consider the
implications of his actions until afterward.  Bruno realizes that he let his friend down,
prompting him to apologize to him.  At the time, Bruno's fear took over and he capitulated.  It
was one of the few moments where  Bruno did not represent what should be as opposed to what is.
 In this moment of panic and fear, he lies to Kotler about knowing Bruno.  It is an instant of
regret, something that he recognizes is wrong, but also something that he does do.  Certainly,
Bruno's instant of fear that makes him lie is offset with his strength and heroism at the end,
when Bruno needs him the most.