In 'Romeo and Juliet', who kills Mercutio?

Tybalt kills Mercutio in 'Romeo and Juliet'. The death occurs during a street confrontation in Act 3, Scene 1, when Tybalt challenges Romeo and Mercutio intervenes on Romeo's behalf.

Romeo tries to prevent the fight because Tybalt has just become his relative through Romeo's secret marriage to Juliet. Mercutio does not know about the marriage and interprets Romeo's refusal to fight as weakness. He accepts Tybalt's challenge, and Romeo steps between them. Tybalt reaches around Romeo and fatally wounds Mercutio.

Mercutio's death is a turning point: Romeo abandons his commitment to peace, kills Tybalt, and is banished from Verona. A frequent mix-up reverses the two deaths. Romeo kills Tybalt immediately after Mercutio dies; Tybalt is therefore Mercutio's killer, while Romeo is Tybalt's killer. Mercutio's dying pun about the houses of Montague and Capulet captures how their feud destroys people who are not directly responsible for it.