I just assumed since it was a corrupt system, and they put him in jail to discredit him, not because he actually committed a crime, that once he signed the confession and had his reputation further ruined, they didn’t need to keep him in fail anymore. Also, they needed him to get out to follow him to Nancy.
You can’t have it both ways. If they wanted to find her, then she was in danger.
And since she was from Sin City, it would have been a natural place for the bad guys to start looking. And she was using her real name. Even pre-Google it doesn’t get much easier than that.
A bit off topic, but I found the opening/closing to be by far the weakest parts of the movie. The dialogue was already pretty stiff, but Hartnet took it to a whole other awful level. About ten minutes in a was worried I was in for a pretty terrible two hours. I was relieved to see him disappear for the other 95% of the movie.
And besides being poorly acted, the whole scene was totally incongruous with the rest of the film. Others here have explained it a bit, but it would either be made to stand alone within the context of the film or excised for a stronger opening.
At least IMHO.
I did really like the movie though, especially the Marv portions.
They wanted to find Cordelia, so they could use her to completely break Hartigan. They didn’t know she was Nancy (although they could’ve guessed). The fact that she was was just gravy.
I’m gonna say it was that a lot of times the parole board will not release you unless you show repentance for your crimes, which if you continue to deny having committed can’t happen. Unfortunately, if an innocent man is convicted, his best chance of early release is to admit to everything.