Justine lives with the Frankenstein family as a servant after her mother dies. When William is murdered, the monster puts a photograph that William was carrying in her pocket, and she is accused of murder. She confesses falsely to the crime out of fear of going to Hell. She is executed.
In addition to the people he actually murders, the monster ends up indirectly causing the death of a few others as well. Justine is the first clear example of this. Alphonse is another. This is interesting. If we start blaming the monster for indirectly causing deaths, then we also have to blame Victor for the same crime. Sure – if the monster hadn’t killed William, Justine wouldn’t have been executed. But, if Victor hadn’t created the monster, the monster wouldn’t have killed William. See? Once you start down that path, you raise all sorts of questions of blame and morality and responsibility. Which is kind of the point of thinking about Frankenstein at all.