In his lecture at the beginning, Jake Hunter (Michael Shannon) says that all known serial killers are male, with the exception to a recent case in the United States. This is a reference to Aileen Wuornos, who was arrested and charged in 1992 for murdering seven men.
Ciarán Hinds and Helen Mirren have worked togther in several other productions: Excalibur (1981), The Cook, the Thief, His Wife & Her Lover (1989), Some Mother's Son (1996), Calendar Girls (2003) and The Debt (2010).