"Moral culpability" is blame that is given to a person who understood that their actions and the consequences of those actions were evil at the time that the acts were committed. To be morally culpable, a person also has to have had control over the situation in which the act was committed.
It is possible for people to commit evil acts but not be morally culpable, if they lack either understanding or control over their actions. For example, if a young child gave a person a poisonous substance to drink without understanding what would happen, they would not be considered morally culpable. Similarly, if a child soldier, even having reached the age of reason, is forced to commit evil acts under mortal danger to himself, his degree of moral culpability would be considerably diminished.