The tension between Paulina's and Roberto's conflicting accounts comes to a head at the end of act 3, scene 1. After having heard Roberto's confession, Paulina announces to him that she is now certain of his guilt. Roberto tries to convince her that the confession was completely manufactured, fed to him by Gerardo based on what Paulina told Gerardo about her experience. However, Paulina claims she was already prepared for that, saying
I knew that he'd do that, I knew he'd use my words for your confession. That's the sort of person he is. . . . But I'm the one who came out on top in this game. I gave him the name Bud, Doctor, I gave him the wrong name, to see if you would correct it. And you did correct it. You corrected the name Bud and you substituted the name Stud.
She confesses that there were "small lies, small variations, that I inserted in my story to Gerardo and you corrected most of them." Although Roberto denies this accusation, it seems unlikely that he would consistently accidentally change his story to match the reality of Paulina's experience.
Caught in this trap, Roberto continues to claim that he is innocent, but in the final moments he seems to falter. He asks Paulina if her executing him wouldn't only perpetuate a cycle of violence and revenge. When Paulina doesn't listen, he tries to stop her, saying
Oh Paulina, isn't it time we stopped?
In this line, Roberto shifts from identifying Paulina and her captor as people separate from himself to addressing them as "we." He thus includes himself in the cycle of violence, and this can be read as an admittance to having played a role in the violence done to Paulina.
Although Dorfman certainly leaves the truth of the matter intentionally vague, the combination of Roberto's knowledge of the reality of Paulina's torture and his slight but telling shift in language after this revelation seem to suggest that Paulina has correctly identified Roberto as her captor.