Answer:
Dr. Frankenstein was not innocent, he purposely set out to create his monster.
Frankenstein's monster on the other hand, was innocent because he was brought up by nature and not nurture (family). He has to fend (manage without help) and learn himself he soon learnt why people hated him.
However, the issue of free will is involved. Is the monster (the one acting) responsible for the death? After all he decided to do it. Victor had no dominion over the monster and he even willed it to stop. He is, in this approach, guilty also.