Death
Death is a main theme of this film. Each of the characters has dealt with death in a major way within the last 24 hours, and death carries on as the Woman commits suicide, the Kid is shot by the police and Donnelly attempts to shoot himself.
Circumstance
Circumstance is a theme in this play in that each character doesn't know the exact circumstances that have happened to the other, especially the Kid and Donnelly to one another. This relates to the fact that we usually react to one another based on what we see, not what we can't see from another person's perspective based on the circumstances of their life.
Identity
Identity is a theme that is seen with the Kid. We know he's young and brash, but we don't know he's a killer until the very end of the film. We learn that he shot his mother in the head, and his last words are only that he regrets not having hit one of the cops during the shootout that claims his life.