In the play, Tybalt seeks revenge on Romeo for sneaking into his uncle's ball and challenges him to a duel in act 3, scene 1. Romeo refuses Tybalt's challenge and attempts to ease the tension, because he has recently married Tybalt's cousin Juliet in secret. Unfortunately, Mercutio stands up to Tybalt, and Romeo intervenes during their struggle. In the middle of the fight, Romeo throws himself between the two men to act as a human barrier, and Tybalt manages to fatally wound Mercutio. Romeo responds with anger and ends up killing Tybalt. Romeo then flees, and Benvolio explains to the Prince what happened when he arrives at the scene.
Lady Capulet immediately demands that Romeo be executed for murdering Tybalt, but Lord Montague points out that Tybalt had broken the Prince’s law first. Lord Montague argues that Romeo only killed someone who would have been executed anyway, and the Prince ends up banishing Romeo from Verona instead of killing him. Judging by Lady Capulet's initial response, Romeo's apology would probably not have relieved the situation or changed her feelings about him. Lady Capulet tells the Prince that "Romeo must not live," which depicts her strong feelings of hatred towards Romeo and his family. Romeo is not only a sworn enemy of the Capulets, but has just murdered their beloved family member. An apology would do nothing to change the situation or their negative feelings. If Romeo were to reveal his secret marriage, the Capulets would more than likely view the situation from a different perspective and possibly entertain the idea of forgiveness. Regardless of whether Romeo offered an apology or not, the Capulets would still resent him and demand that he die. The Prince would also follow through with his alternative punishment, and Romeo would still be exiled.