<P> Roman trades Frost to Sabian in exchange for restoring the building's electricity, having been turned off after the hostage execution . With help from Rudy and Maggie, Roman accesses Niebaum's computer and pieces together the scheme; corrupt officers submitted false disability claims that were processed by an unknown insider on the disability fund's board . He also discovers recordings of wiretaps, including a conversation that suggests Roenick was meeting his informant before he was killed . Sabian, using the information Roman provided, claims to have located Roenick's informant in a bid to get Roman to release the hostages . Roman realizes Sabian is bluffing when Niebaum's files reveal Roenick himself was the IAD informant . </P> <P> When Roman threatens to expose Niebaum in an open window, leaving him vulnerable to sniper fire, Niebaum admits that Roenick gave him wiretaps implicating three of Roman's squad mates, Hellman, Allen, and Argento in the embezzlement scheme . When Niebaum confronted the guilty officers, he received a bribe from them to cover up their crimes . They offered Roenick the same money, but when he refused to take it, their inside ringleader murdered him . Niebaum says he doesn't know who the ringleader is, but that he has the taps corroborating the three officers' guilt . The same corrupt officers have secretly entered the room via the air vents under the pretext of being part of a team to take Roman out in case he started killing hostages; upon hearing Niebaum's confession, they open fire and kill Niebaum before he can reveal where he has hidden the wiretaps . Roman single - handedly fends them and the rest of his squad off, using the flashbangs he seized from the two officers in the previous failed breach . </P> <P> Believing that Sabian and the police cannot resolve the situation, the FBI assume jurisdiction over the operation, cease negotiations, relieve Sabian of his command, and order a full breach . As Roman prepares for his eventual arrest, Maggie tells him that Niebaum also worked at his house and could have kept Roenick's wiretaps there . Sabian confronts Roman to warn him about the breach, and Roman reveals that the corrupt Officers murdered Niebaum and the executed hostage is still alive and gagged . Sabian begins to believe in Roman's innocence and gives him a chance to prove his case: while the FBI and SWAT raid the building and rescue the hostages, Roman disguises himself as a SWAT member and escapes . Roman and Sabian proceed to Niebaum's house, but they can't find the wiretaps . The police arrive and the corrupt officers enter the house, but they back off as Frost enters and tries to talk Roman down . Sabian observes Frost discreetly taking one of the loaded guns, and realizes that Frost is the ringleader of the conspiracy, the insider on the disability fund's board and Roenick's killer . </P> <P> In front of Frost, Sabian seemingly kills Roman and offers to destroy the evidence they have uncovered in return for a cut of Frost's take . Frost agrees and effectively makes a full admission to his and the other three officers' crimes . When Frost exits the house, he discovers that Sabian only wounded Roman who used a police radio microphone to broadcast his confession to the police surrounding the area . Humiliated, Frost attempts to commit suicide, only to be foiled and arrested by the police . As Roman is loaded into an ambulance, Sabian gives his badge to him and departs . </P>

Who is the bad guy in the negotiator