To prepare for the role of Gerry Conlon, Day-Lewis lost over 23 kilograms (50 lb) in weight. To gain an insight into Conlon's thoughts and feelings at the time, Day-Lewis also spent three days and nights in a jail cell. He was prevented from sleeping by a group of thugs, who would bang on the door every ten minutes with tin cups through the night, then he was interrogated by three different teams of real Special Branch officers for nine hours. He would also insist that crew members throw cold water at him and verbally abuse him. He also kept his Belfast accent on and off set.
Day-Lewis has stated in an interview that he went through all this because otherwise "How could I understand how an innocent man could sign that confession and destroy his own life."[4][5]
