Jimmy McNulty

Season one

Before the start of the series, McNulty has noticed that drug kingpin Avon Barksdale is expanding his organization's territory, and that his gang has successfully beaten several murder prosecutions. After Avon's nephew D'Angelo is acquitted thanks to witness tampering, McNulty goes over the head of his superior, Major William Rawls, and convinces Judge Phelan to call Deputy Commissioner Ervin Burrell and encourage further investigation of the Barksdales. Because of McNulty's efforts, the Barksdale detail is officially formed, initially consisting of Narcotics Lieutenant Cedric Daniels and detectives Kima Greggs, Ellis Carver, and Thomas "Herc" Hauk.

When Burrell asks his majors and shift lieutenants to send additional detectives for the investigative detail, McNulty himself is also assigned to the unit. Daniels and McNulty argue about how to handle the case at their first meeting: McNulty, after seeing an FBI drug sting, suggests surveillance and wiretaps, but Burrell has ordered Daniels to put together a quick and simple case to appease Phelan. Soon after the investigation begins, McNulty learns from his friend in the FBI, Special Agent Fitzhugh, that Daniels had been investigated for having a suspiciously large amount of liquid assets. His relationship with Daniels continues to be complicated by their mutual distrust.

The detail is assigned Assistant State's Attorney Rhonda Pearlman as a prosecutor, with whom McNulty is having a casual sexual relationship. McNulty is officially separated from his wife, who limits his contact with his two sons, Sean and Michael. While shopping with them one afternoon, McNulty spots Russell "Stringer" Bell, Avon Barksdale's second-in-command, and sends his sons to tail him and get his license plate number. When Elena finds out, she seeks an emergency order to stop him from seeing them. She is also angry that he continues to see Pearlman casually.

Working on the Barksdale detail, McNulty becomes friends with Lester Freamon, who had previously been exiled to the pawn-shop unit for thirteen years and four months for his insistence on charging a politically connected fence. Freamon often tries to temper McNulty's animosity towards Daniels. Frustrated that Barksdale's dealers do not use cell phones, they decide to clone the dealers' pagers instead. They also work together to convince Daniels to allow them to do better police work.

With the help of Kima, McNulty tracks down the elusive outlaw Omar Little, gaining his respect and cooperation. Omar agrees to testify against Marquis "Bird" Hilton, a Barksdale soldier. His assistance also leads to McNulty inadvertently solving one of Michael Santangelo's old cases; a grateful Santangelo in turn reveals that he is a mole for Rawls, who is looking for an excuse to fire McNulty. Kima introduces McNulty to her confidential informant, Bubbles. When she is shot in a buy-bust sting operation gone wrong, McNulty is guilt-ridden, though even Rawls assures him that the shooting is not his fault. McNulty has a frank discussion with Daniels in which he admits that the Barksdale case is no more than an exercise in intellectual vanity and an opportunity to demonstrate the BPD's shortcomings. Daniels tells him that everyone has known this all along but that the case has taken on meaning for those involved.

The detail succeeds in arresting Barksdale soldier Wee-Bey Brice for shooting Kima, Bird for murdering a state's witness, and both D'Angelo and Avon Barksdale. McNulty almost convinces D'Angelo to testify against Avon but, ultimately, D'Angelo takes a twenty-year prison sentence instead. When the Barksdale detail closes, Rawls reassigns McNulty to the marine unit, having learned from Sergeant Jay Landsman that this is precisely the BPD unit where McNulty does not want to go.

Season two

While on harbor patrol, McNulty spots the body of a dead woman in the water. When Rawls argues the case is not in his jurisdiction, McNulty, spends three hours poring over wind and tide charts to prove the death occurred within city limits. When port authority officer Beadie Russell finds thirteen dead women in a shipping container on the Baltimore docks, McNulty again intervenes and, with the help of the medical examiner, proves that the deaths were not accidental: the air pipe to the container was deliberately closed off, and, with the help of a mining engineer, they are able to prove that the ship was within the city limits when it happened. The case is given to Bunk and Lester, who don't look forward to investigating these difficult cases.

McNulty unsuccessfully searches for the identity of the floater. He also finds himself under pressure from Bunk to find Omar, since Bird is about to go on trial. McNulty coerces Bubbles into tracking down Omar, who testifies against Bird. Meanwhile, McNulty signs an agreement that he will pay alimony to Elena, even though he believes his marriage is still salvageable. He resolves to give up alcohol and detective work, two of the main reasons for the breakup of his marriage. When Elena confirms the marriage is over, he grows despondent and relapses.

When Daniels's unit is re-formed to investigate stevedore union boss Frank Sobotka, Rawls refuses to allow McNulty to rejoin the team. McNulty seems to accept this with good grace, but tries to help the detail unofficially. Daniels persuades Rawls to let McNulty return by taking on the murders of the fourteen women. McNulty's first assignment is to go undercover as a client visiting a local brothel, much to the amusement of his colleagues. He also flirts with Russell, who has been assigned to Daniels' detail, though he seems to shy away from a relationship.

While on surveillance, McNulty watches Spiros Vondas, an associate of an underworld figure known as The Greek, sending a text message. He reasons that the time and location of the text could be used to retrieve it from the phone company's databases; it is from this message that the detail learns that the Greek had shut down his operations. After McNulty learns from Bubbles that Stringer Bell and Barksdale rival Proposition Joe are sharing territory, he begins investigating them on his own time, convinced that he can gather enough evidence to prompt Daniels to focus the Major Crimes Unit's attention on Stringer.

Season three

McNulty continues to work with the MCU, but is disappointed that their target is not Bell. He begins looking into the Barksdales anyway, finding out about D'Angelo's death and Avon's early release. Investigating D'Angelo's death, he quickly realizes that D'Angelo was murdered. McNulty reconnects with Colvin to set up the Barksdale organization as the MCU's primary target. McNulty circumvents the chain of command again to set up the investigation, as Daniels is not interested in the quality of the unit's assigned case targets, blaming his rank in the department for his lack of case target interests. Angered by McNulty's attitude, Daniels tells McNulty that he'll be finished in the unit when Stringer is arrested.

McNulty begins a relationship with political consultant Theresa D'Agostino, but realizes that she is only interested in him physically and is pumping him for information about Colvin. Largely due to Freamon's work, the MCU implicates Bell, but he is murdered before McNulty can arrest him. After Avon is arrested, Daniels reevaluates his decision to get rid of McNulty, but he realizes he has no life outside his work and graciously declines Daniels' offer to keep him in the unit. He transfers to patrol in the Western District, which he remembers as the happiest time of his life, and begins a relationship with Russell.^[1]

Season four

McNulty moves in with Russell and her two children, and enjoys his life as a patrolman in the Western District under Ellis Carver. His beat includes the corner that Bodie works on behalf of drug kingpin Marlo Stanfield. Both Daniels and Administrative Lieutenant Dennis Mello ask McNulty to do investigative work in the district, but he declines. Mello is disappointed but Daniels realizes that McNulty has been able to get his life in order while working as a patrolman. Though other officers make arrests for statistical purposes, McNulty focuses on quality arrests. This is exemplified by the arrest of two burglars who were stealing from churches.

McNulty mentors Brian Baker, a younger patrol officer in the Western, whom he and Bunk end up referring to as "good police". He also significantly reduces his drinking, sometimes resolving to stay sober despite pressure from his friends. Bunk and Freamon are amazed and slightly dismayed at how much McNulty has changed, and Elena even expresses regret for having left him. McNulty soon begins to miss the MCU, and quietly begins getting closer to Bodie in the hopes of turning him into an informant against Marlo. After Stanfield lieutenant Monk Metcalf sees Bodie with McNulty, Bodie is killed as a precaution. McNulty feels guilty and rejoins the MCU, much to the delight of Freamon and Daniels. It is revealed during a scene shortly after Bodie's death that McNulty feels he "owes it to the kid".

Season five

With the BPD scaled back due to Mayor Tommy Carcetti's budget cuts and the vacant murders unsolved, McNulty is despondent and falls back into old habits.^[2][3] Shortly after being transferred back to Homicide, he visits the morgue and finds two county detectives arguing with the medical examiner and subsequently learns that pre-mortem and post-mortem strangulations are forensically indistinguishable. While investigating a probable overdose case with Bunk, McNulty tampers with the crime scene to make it seem that a struggle occurred. Over Bunk's protests, McNulty strangles and stages the corpse to make it appear as if a "serial killer" has come to Baltimore.^[4][5]

McNulty sets out on his ruse in the hopes that the "case" secures more funding for Homicide and the Stanfield investigation. He doctors case files and plants evidence in order to link them together and create the impression of a serial killer targeting homeless men. When Landsman ignores the case, McNulty approaches reporter Alma Gutierrez of The Baltimore Sun, but only succeeds in the story getting printed in the middle of the paper instead of the front page. Bunk repeatedly warns McNulty against his self-destructive course; Lester, however, approves of the endeavor and suggests that it needs sensationalism to succeed.^[6][7]

When McNulty finds that most dead homeless men are concentrated in the Southern District, Freamon puts him in touch with an old patrol partner there who agrees to tip them off when new bodies are found. Freamon also devises a plan to show maturation in their serial killer's pattern and acquires dentures to create bite marks on the victims, thus enhancing the media appeal for the story. While canvassing an area frequented by local homeless, McNulty complains that Landsman barely noticed his work on the case, but Freamon reminds him that if their plan works, the case will attract more interest and sloppiness could be their downfall. Upon returning home, McNulty is confronted by Russell over his drinking and philandering.

Upon finding a new body, McNulty mutilates the decedent to show bite marks and defensive wounds.^[8] When investigating the "homeless killer", McNulty and Greggs travel to the FBI Academy in Quantico, Virginia for assistance. McNulty realizes that he can no longer falsify the murders on real corpses as there is too large a police presence, so he instead takes a mentally ill homeless man off the streets and stages a photograph of a murder to send to Sun reporter Scott Templeton, before taking the man to a homeless shelter in Richmond with fake identification.

McNulty has been voicing the killer in telephone calls to Templeton. After doing the voice analysis, the FBI provides McNulty and Greggs with a psychological profile of the homeless killer, inadvertently giving a near-perfect description of McNulty himself. Having his character flaws spelled out for him gives McNulty second thoughts about what he has done. He confesses his deception to Greggs, who in turn informs Daniels, now the BPD's Deputy Commissioner for Operations. Daniels and Pearlman subsequently meet with Acting Commissioner Rawls, State's Attorney Rupert Bond, and the mayor's office. Daniels and Rawls confront McNulty, informing him that this will be his last CID case.

The case is "solved" when McNulty encounters a mentally ill homeless man who has started using the modus operandi of the phony serial killer. McNulty brings the man, his final criminal, to justice. McNulty and Freamon then leave the police department. After attending a detective's wake (of sorts) in their honor, McNulty leaves the bar sober and returns home, where he and Russell have reconciled. The next day, McNulty returns to Richmond, finds the homeless man he had put there, and drives him back to Baltimore. On the way back, he stops his car, gets out and looks at the city, leading to the series-ending montage.