 The show centers on FBI special agents who work on cases linked to the paranormal , called X @-@ Files ; this season focuses on the investigations of John Doggett ( Robert Patrick ) , Monica Reyes ( Annabeth Gish ) , and Dana Scully ( Gillian Anderson ) . In this episode , Doggett is determined to find an error in the DNA evidence that freed the convicted Robert Fassl , the " Screwdriver Killer " , whom he nearly caught in the act 13 years earlier . In the end , it is revealed that Fassl has a mental condition that splits him into two parts : the religious innocent and the vengeful killer . 
