Factual error: The movie opens on Halloween in Brooklyn. To show how crazy things were in Brooklyn, they show a baseball game being played by the Brooklyn Dodgers that day at Ebbetts Field and a big fight breaks out. The baseball season is and was over (including the World Series) well before Halloween. So there is no way they could be still playing on Oct 31st The only exception was in 2001 when games were postponed due to the 9/11 attacks and the season didn't end until November.
Character mistake: The plain clothes officer who arrives is referred to by his officers as "Lieutenant", but Mortimer calls him "Captain" more than once.