 He recalls a childhood memory when he sustained child abuse at the hands of a foster parent.Aldo killed the man, which affected Michael greatly.This flashback also explains the source of Michael's low latent inhibition (which enabled him to formulate and execute the escape plan) and low self-worth (which is what made him go to such extreme lengths to help his brother in the first place), both of which were first alluded to in the first season episode "Tweener".