Ruth Wilson was cast as Joe Durkin (who is a male character in the books) and filmed all of her scenes as Liam Neeson's partner. But the director felt that Neeson's character should be a loner so all of Wilson's scenes were cut.
There are two separate scenes which show the New York City skyline. The first is a panoramic view showing, from right to left, the Chrysler Building and the Empire State Building. At the end of the film, a similar skyline is shown but shows both towers of the World Trade Center. The first view does not, despite the film taking place between 1991 and 1999. The World Trade Center was not destroyed until 2001 on September 11th.
(at around 6 mins) The year jumps from 1991 to 1999. As soon as the year changes to 1999 Scudder is sitting in the diner reading the Daily News. However, the back page of the newspaper is a story about a Seton Hall Pirates basketball game from 1991 (the front page looks to be era correct as there is a story about Y2K).
At the beginning of the movie Scudder is firing an M1911 pattern pistol at the fleeing robber. There is no similar weapon on the approved carry list for a regular (carrying a badge and not undercover) officer of the NYPD.