Did Prendergast really retire?
Towards the end of the movie, when Sergeant Prendergast is sitting on the front step talking to Adele, he tells her that his name is "mud", and then Adele (as most young children would do), thinks it would be funny to have such a name and says that this isn't his real name. Then, Sergeant Prendergast says, "Well, it will be. Once my wife finds out that I'm still a cop."
This line suggests that Sergeant Prendergast decided that he was not ready to retire after all (much to the dismay of his nagging, worrywart of a wife).