In preparation for his role, Daniel Day-Lewis lost thirty pounds and spent nights in the jail cell on the set as crew members threw water and verbal abuse at him.
Despite playing father and son, Pete Postlethwaite was only eleven years older than Daniel Day-Lewis.
In real life, Gerry and Giuseppe did not share a prison cell and were usually kept in separate prisons.
Daniel Day-Lewis kept his Northern Irish accent on and off the set for the entire shooting schedule.
The character of Inspector Robert Dixon is a combination of several police officers connected to the case.