Szymanski first appeared investigating the murder of Benny D’Agostino at a bodega who was the prime suspect in a series of murders of Russian mobsters. He helps Carter and Fusco investigate the case by interviewing his widow Patti D’Agostino where she reveals Carl Elias' intentions to avenge his murder. Later a call comes in about a shootout involving the Russians and a witness named Charlie Burton who was present during Benny's murder. They eventually capture Peter and Laszlo Yogorov only to realize that Charlie is the mob boss Elias. (“Witness”)
As he was an honest cop, Carter entrusted him with the job of guarding Gianni Moretti, Elias' father. Ultimately, Reese revealed Moretti's location to Elias in order to save a person of interest, and Szymanski was severely injured in the line of duty and taken to the hospital. (“Baby Blue”) Fortunately, he survived. (“Identity Crisis”)
After being asked by Finch about Lou Mitchell, Carter has Szymanski look into his past. Szymanski explains Lou's criminal history and notes that the area Lou used to work contains the Venus Casino run by Dario Makris who is under investigation by the narcotics division.
In order to make a deal with Peter Yogorov for backing from the Russian Mafia, HR frames Szymanski as a dirty cop to discredit his testimony by planting money on him, buying a condo in his name in Florida and opening a Cayman Island bank account for him and then having one of Cal Beecher's CIs tip him off. However, Carter refuses to believe Szymanski is dirty and on a suggestion from Fusco, follows the money found in Szymanski's apartment. Carter discovers the marked bills had been placed by the FBI in a bodega run by Elias that had been raided by the NYPD six days later. The marked bills had never showed up in evidence and Carter suggests that a dirty cop stole them which gave HR the perfect way to frame a good cop. With this new evidence, Szymanski can be released on bail by the end of the day and testify against the Yogorovs while also getting IAB off his back.
Szymanski and ADA Melinda Wright later meet with the mayor's Chief of Staff Alonzo Quinn who wants to know about their plans for the trial against the Yogorovs. Both Szymanski and Wright are determined to forward with the trial and have added charges of witness tampering to Peter Yogorov. Telling them that "that's what I wanted to hear", Quinn pulls a gun and shoots Szymanski and Wright twice, killing them both. He then has Raymond Terney shoot him in the right shoulder to make it seem like an unknown assailant killed Szymanski and Wright and injured Quinn. (“All In”)
After Szymanski's death, Finch visits Elias in prison who tells him that Szymanski and Wright's murders benefited his enemy, Peter Yogorov. Carter becomes suspicious that Beecher is corrupt and a member of HR given the timing, leading Fusco to confront Beecher. Beecher, rattled visits Quinn who gave him the tip and Quinn eventually claims that one of Elias' soldiers told him about Szymanski being corrupt. To find out the truth, Beecher visits Elias to find out if Szymanski had been working for him. Elias raises questions about who could've been powerful enough to frame Szymanski and finally tells Beecher that Szymanski was in fact a clean cop. Elias had once tried to bribe him, but Szymanski threw the money back in his face. As a result, after realizing that Beecher is getting too close to the truth, Quinn has him killed too while Fusco is able to clear Beecher's name to Carter by using a forced pairing of Beecher's phone to record the conversation for her. (“Trojan Horse”)
- In the simulation where the Machine was not created, Szymanski was still alive and working in NYPD 8th Precinct. When Fusco visited him, Szymanski was disgusted to see him as Fusco had only avoided jail time as he was the first cop to turn on HR. While disgusted by Fusco's work, Szymanski told him he was probably better off as crime had dropped so much all the homicide detectives were doing was solving cold cases using an updated DNA database. (“.exe”)