A JUSTIFICATION FOR THE MURDER AT THE END OF THE COMEDY. Mary Jane’s explanation for the ending is that Measure for Measure is about the tension between justice and mercy. The text of the play presents the Duke as coming down at the end of the play entirely on the side of mercy and ignoring justice. At the end of the play, the Duke as an exercise of mercy pardons Barnardine, who is a murderer. The director, in choosing to have Barnardine kill Isabella, is making a plea that justice should not be entirely forgotten.
I looked up the Chicago production on the internet and found this article by Emmet Sullivan in Chicago magazine, which focuses on the last two seconds of the production. Sullivan interviewed Robert Falls, the director of the production, and reports that the ending grows out of the director’s view that the duke is “an egocentric, incompetent ruler”. Falls explained: “He has just pardoned a murderer in front of people, in effect saying, ‘Hey, look at how merciful I am.’”