Mary Shelley characteristically complicates the moral lines here. Even as Justine
is called a "monster," she resorts to her own habitual modes of religious instruction
to categorize the behavior of the murderer. That she happens to use the same terminology
as Victor does is a nice irony. But if we then seriously accept his own claim of ultimate
responsibility for this debacle, Justine's invocation of the devil is tantamount to
an ironic accusation against Victor, implicitly inverting his earlier (I:3:8) moral
exoneration of himself as a godlike creator.