Character mistake: In the court scene Clyde mentions a case, Day v McDonough docket number 04-1325. This is a real case, but the docket number is 04-1324.
Character mistake: Clyde enters his cell in the final scene, and is surprised to find that he has been found out. His secret tunnel, if we go according to the characteristics accredited to his character throughout the movie, is surprisingly without any alarms of any sort. Very strange if we are to believe he is as deadly as credited. He ends dying a very silly death.
Answer: Because Nick knows this man is guilty. He says it to almost imply, "well since I'm getting off, may as well make a visit to your family next. You married, Nick?"