It isn't clear how involved Gertrude is in the murder of her first husband. She marries Claudius only a few months after the king is murdered, but the Ghost of Hamlet's father tells Hamlet not to harm her. Wouldn't King Hamlet's want revenge on her as well if she had been a part of it? She is dependent on Claudius and is easily manipulated by him, so she could be easily fooled by him. In Act I, the Ghost denounces Claudius for seducing Gertrude. Critics disagree whether this means Gertrude was having an affair before the king's death, or if the Ghost was referring to their marriage after his death. By the final scene, Gertrude seems to suggest that she was unaware of the crime. This is one of those questions where you could make an argument either for or against Gertrude's involvement.