Who is wrongly executed for the murder of William Frankenstein?

Justine Moritz is wrongly executed for the murder of William Frankenstein. The creature kills William, Victor's young brother, then plants a miniature portrait belonging to William on Justine, making her appear responsible for the crime.

Justine is a servant and family friend of the Frankensteins. Because she had been searching for William after he disappeared, suspicion falls on her when the portrait is found among her possessions. She is arrested, tried, and convicted despite maintaining her innocence.

Victor knows—or strongly suspects—that the creature committed the murder, but he does not reveal what he has seen. He believes no one will accept his account of a living being created in a laboratory. His silence contributes directly to Justine's execution and becomes one of the novel's clearest examples of his failure to take responsibility.

Justine eventually confesses after pressure from her priest, although she later explains that the confession was false and made under fear. The episode highlights the novel's concerns with prejudice, unreliable justice, and the devastating consequences of Victor's secrecy.