Detective Kenny Daniels was an officer of the NYPD. He worked with Ed Green in the mid-1990s.
Background
In 1979, Daniels arrested a man named Walter Grimes for robbing a liquor store at gunpoint. When the store owner was brought in to identify Grimes, he insisted that the robber was Latino and the case was eventually dropped. In 1983, Daniels investigated Grimes for the murder of a 16-year-old girl named Julie Sayer after witnesses placed him with Sayer on the morning she was killed. Grimes continually berated Daniels and even tried to punch him, but Daniels dodged and beat him in retaliation. Afterwards, Grimes confessed to slitting Sayer's throat and even told Daniels the knife was in a storm drain. The arrest was, however, voided after Daniels' lieutenant saw what Daniels did to Grimes. Daniels decided to get the knife from the storm drain himself and use it to frame Grimes for another murder later on.
When another girl named Leanne Testa was stabbed to death, Daniels decided to use the knife to frame Grimes for her murder since both were stabbed with the same type of knife and had the same blood type. Daniels called in an anonymous tip that Grimes was the murderer and pretended to find the knife in Grimes' closet to frame him. As a result of his actions, Grimes was convicted of second-degree murder a year later. Daniels later earned his detective's shield and worked at multiple precincts. Green and Daniels worked together as partners at the 29th Precinct in the mid-90s and Daniels kept Green in line, often calling him a "cowboy". Meanwhile, Grimes had DNA testing done on the knife and he was exonerated for Testa's murder.
Vendetta
In 2004, Daniels is interviewed by ADA Serena Southerlyn about Grimes' past crimes after he kills a man named Brendan Donner. Daniels tells Southerlyn that they should never have let Grimes out despite the fact that he was exonerated. Southerlyn then questions him on Grimes' history as a criminal. Daniels insists that Grimes was guilty of the robbery, despite the original witness statement pointing out flaws in his logic. Green eventually visits Daniels at his home to question him about his conduct during the investigation into Testa's murder. Daniels continues to swear Grimes did the robbery. When Grimes asks about the knife, Daniels explains his history with Grimes and his role in Sayer's murder and planting the evidence. Daniels defends his actions as getting Grimes locked up for Sayer's murder in order to atone for the mistake he made.
The DA's Office eventually charges Grimes with both murders after getting the knife back in as evidence in Sayer's murder case. They call Daniels to testify in Sayer's murder case, but Daniels repeatedly refuses, explaining that he feels remorse for getting Grimes locked up in the first place. EADA McCoy argues with Daniels, saying that he put himself above the law and that he must now testify about his remorse. Daniels eventually agrees and testifies at the trial, explaining everything that had happened. He even says that he regrets his actions back then. Grimes' attorney, Rodney Fallon, cross-examines him, arguing that even though he is losing his pension and destroying his own career, he will do anything to see Grimes locked up.
As Daniels is leaving, he tells Green that after what he did to Grimes, they aren't friends anymore. Green tries to point out that they had no choice to get justice for Sayer, but Daniels says he already had justice for her. After Grimes eventually accepts a plea for both murders, Green meets Daniels in a bar to tell him the news. Daniels replies that he had been encouraged to take an early retirement. Green expresses his condolences, but Daniels says it was the result of doing what he needed to do. What Daniels doesn't realize is that by framing Grimes for Testa's murder, he allowed the actual killer to get away.