Whose dagger kills Juliet? What might this symbolize? How does the symbol reflect responsibility for Juliet's death?

Romeo's dagger kills Juliet. This symbolizes a communion between the two lovers; it is a communion that is both sexual and spiritual. It must be Romeo's dagger that kills her because she wants an eternal union with him. To some extent Romeo is the impetus for her own death. Romeo's impulsive drinking of his poison causes Juliet to end her own life.