|Original Airdate||March 10, 2005|
Compulsion is the seventeenth episode in the fifth season of CSI.
A budding serial killer strikes again, and the CSI team tries to use new technology to solve a cold case. Nick and Catherine investigate the murder of a young boy found dead in his bed. His brother confesses to the killing, but evidence suggests that he may not have committed the crime.
Gil Grissom and his team investigate a case in which a female flight attendant has been violently raped and stabbed to death in her hotel room, in which Conrad Ecklie discovers parallels to a five year old cold case. Modern background removal techniques enable the CSIs to recover a fingerprint that leads them to a serial offender. Despite a judge denying their request for a warrant, the CSIs manage to acquire the suspect's DNA, which doesn't match semen found at the crime scene. Analysis of this semen indicates that the likely suspect had undergone a vasectomy reversal.
Whilst interviewing the hotel manger to discuss bleach found at the scene, Grissom notices that the manager's children's ages significantly differ. A question about his vasectomy leads the manager to clam up and refuse to provide a DNA sample. In the interview room at the police station, Grissom tells the suspect and his lawyer about premeditated psychopaths. As the lawyer is pointing out they have no evidence tying the suspect to the crime, Sara Sidle wheels in a suitcase, the sight of which causes the hotel manager to accuse the police of breaking into his car. His lawyer says that if they did break into his car to retrieve the suitcase, the entire case must be thrown out. Sara opens the suitcase and reveals that it is identical to the victim's, with nothing but a tape recorder inside. The hotel manager's words, however, have already given the CSIs probable cause to search his car, sealing their case.
Meanwhile, Catherine Willows' team assists Detective Cavaliere in the investigation of a young boy who was savagely beaten to death with a pipe while in his own bed. Nick Stokes and Cavaliere get into a heated argument over their methods of finding the culprit. Cavaliere gets a confession after coming down hard on the brother of the victim—too hard, Nick believes. Nick decides to investigate the evidence, turning up a neighborhood bum who has been causing a nuisance. He is found wearing the boy's father's blood spattered jumper. Unable to pick between the bum, the father or the boy's brother, the team beat a bloody mannequin to gain insight as to the likely suspect. The pattern of the spatter leads them to identify the boy's brother as the killer. After meeting with the father, the brother admits it was because the victim told everyone about him wetting the bed.
Grissom expresses pleasure with the work Greg Sanders, Sara and David Hodges put in to investigating the case. Hodges admits to sniffing the bleach at the hotel, asking Grissom if he thinks it's odd. As the bleach was unique in its composition, a fact made evident by its odor, Grissom replies that it is the first thing Hodges has done to impress him.