Leander Sydnor is a Detective in the Baltimore major case unit. Sydnor is played by Corey Parker Robinson.
Earlier in the series, Sydnor is noted as being one of the best younger detectives on the force. A good investigator with a thorough knowledge of the streets of Baltimore, Sydnor is used frequently as the Major Case Unit's undercover officer in street based operations. Sydnor is shown preferring to do good investigations using workable interrogation tactics to make a case. Sydnor seems to be disliking of the Baltimore Police Department's method of case selections as he has had disagreements over the choice investigation targets due to departmental politics. It seems that Sydnor like Detective Pryzbylewski is more interested in investigations than in making rank but unlike Prez, he seems to enjoy the tactical hand to hand methods of policing more than the asset investigation based methods of policing. Realizing the demands of the detectives, Sydnor appears mentoring the other young plainclothes officers in his units throughout the series as his police skills and street knowledge have proven him to be one of the smartest younger detectives on the force. Throughout the series, he appears to be working best with Detectives Prez, Greggs, Herc, Massey and Dozerman under the command of Lester Freamon or Cedric Daniels.
Sydnor is a young, married Baltimore Police detective and was a member of the Barksdale detail and later worked in the Major Case Unit. Sydnor was assigned to the Barksdale detail after Lt. Daniels made a special request of Sydnor's commanding officer Lieutenant Cantrell to give him his best detective to balance out taking the erratic Detective Pryzbylewski. In the Barksdale detail he often worked with Detective Lester Freamon who became something of a mentor to him. He helped Freamon to dig into the Barksdale organization's paper trail. Sydnor also performed valuable undercover work alongside Detective Kima Greggs and her informant Bubbles. Bubbles helped Sydnor improve his undercover image by recommending changes like wearing out his shoes and not wearing his wedding band. His undercover work involved making hand to hands to build evidence. Sydnor was responsible for identifying Avon Barksdale at a basketball game. He later told Daniels that the investigation was the best police work he had ever done.
Sydnor returned to working in his old district after the dissolution of the Barksdale detail. When Daniels established a permanent Major Case Unit he was allowed to choose his own detectives and encouraged Sydnor to transfer in. Sydnor took up the offer and again worked on investigating the Barksdale organization.
In Season 4, the Major Case Unit was investigating Marlo Stanfield in addition to the Barksdale money trail. With Daniels promoted to Major, Lester Freamon was the guiding force behind the unit and had hand-picked their shift lieutenant Jimmy Asher, a retiring officer who took a non-interfering approach to the unit's investigations. The money trail led them to major political figures which worried Sydnor. Sydnor personally delivered a subpoena for financial records to State Senator Clayton "Clay" Davis despite worries about how this would impact on his career. 
Senator Davis angrily protested the subpoenas to Mayor Clarence Royce who then threatened Commissioner Burrell to get the Major Crimes Unit under control. Deputy Rawls then suggested "proper supervision" for the unit and replaced Lieutenant Asher with Lieutenant Charlie Marimow, a caustic commander with a reputation in the department as a "unit killer." Marimow's command style drove away Freamon and Greggs leaving only Sydnor and Massey in the unit. Opting to leave the unit at the first available opening, Sydnor remained in the unit. With the transfer of Detectives Herc and Dozerman, Sydnor found himself two allies looking to make cases while maintaining a dislike for Marimow. The unit was unsuccessful making cases under Marimow as there was little evidence present to successfully build strong cases against westside drug dealers. Sydnor mentored Dozerman over the course of the season and advised Herc of the cautions in lying to Marimow. The unit was then recreated under Cedric Daniels who was promoted to CID colonel, allowing Freamon carte blanche in leading Major Crimes. Under Freamon's leadership, Asher was named Shift Lieutenant again, and Jimmy McNulty and Kima Greggs transferred back into the unit. As the season ended, a new investigative strategy was mapped out against Marlo Stanfield.
After more than a year of investigation into the Stanfield Organization, the unit still did not have a strong enough case to file charges. When budget cuts in the department eventually led to the unit being closed down, Sydnor was disappointed to find his work wasted and realized that simply keeping Stanfield under surveillance was effective in reducing crime. Sydnor and Lester Freamon were detailed to the State's Attorney's office to prepare the corruption case against Clay Davis. Sydnor and Freamon first prepared the paperwork on Davis and then assisted Rhonda Pearlman in a series of Grand Jury depositions.
Sydnor uncovers evidence of Davis having committed a federal crime when he finds that Davis borrowed money from his mother for a mortgage deposit. Freamon realizes the significance of the crime and is aware that it could warrant a thirty-year jail term. The detectives present the evidence to State's Attorney Rupert Bond and he refuses to take the case federal as he wants to prosecute Davis himself for political reasons.
In the series finale ("-30-"), Leander Sydnor visits Judge Daniel Phelan in his chambers to apply back-channel pressure in order to advance an investigation, much like McNulty did in Season 1. This suggests a parallel between Sydnor and McNulty, since Sydnor now shows interest in going around the rules to advance a case or push a more important agenda.
|Season 1 appearances|
|"The Target"||"The Detail"||"The Buys"||"Old Cases"||"The Pager"|
|"The Wire"||"One Arrest"||"Lessons"||"Game Day"||"The Cost"|
|"The Hunt"||"Cleaning Up"||"Sentencing"|
|Season 3 appearances|
|"Time after Time"||"All Due Respect"||"Dead Soldiers"||"Amsterdam"||"Straight and True"|
|"Homecoming"||"Back Burners"||"Moral Midgetry"||"Slapstick"||"Reformation"|
|"Middle Ground"||"Mission Accomplished"|
|Season 4 appearances|
|"Boys of Summer"||"Soft Eyes"||"Home Rooms"||"Refugees"||"Alliances"|
|"Margin of Error"||"Unto Others"||"Corner Boys"||"Know Your Place"||"Misgivings"|
|"A New Day"||"That's Got His Own"||"Final Grades"|