(at around 8 mins) The photograph on the bulletin board at the guard desk that Martin notices when he shows up for his first shift and asks the old watchman about, is a famous photo of Lewis Thornton Powell (also known as Lewis Paine or Lewis Payne), a conspirator with John Wilkes Booth, the assassin of Abraham Lincoln.
The movie is a remake of the Danish movie Nightwatch (1994). The director of the Danish original, Ole Bornedal, also directed the remake.
The opening scene where a prostitute gets violently murdered was not part of Ole Bornedal's original cut, presumably being added by Dimension during the post-production phase. The scene only includes Anais Evans, who does not appear in the rest of the film, and who has not had any other acting roles.
Dimension wanted to reshoot several of Ewan McGregor's scenes after his character received low scores from audiences in test screenings. McGregor refused to do so.
(at around 8 mins) The black and white picture of the guy on death row in the cabin is the same one used in the original version of this movie (Nightwatch (1994)).