Brooklyn's Finest

Bobby "Carlo" Powers and Detective Salvatore "Sal" Procida are having a conversation in a car when Sal unexpectedly shoots Carlo, grabs a bag of money from Carlo's lap and flees, then confesses to a priest, asking for help with his dire situation; his wife is pregnant with twins, in a house too small for their four children and has wood mold, which jeopardizes his family's health. Desperate to move, Sal has arranged to purchase a larger home through a woman who owes him a favor. The down payment is due the following Tuesday, and Sal is still short. Sal is a highly skilled and accomplished narcotics detective, but has begun to pocket drug money from raids.
Officer Edward "Eddie" Dugan is a week from retirement after 22 years of unremarkable service to the force. He is assigned to oversee rookies in the tough neighborhoods. His life in shambles; he swills whiskey in the morning to get out of bed and his only friend is Chantal, the prostitute he frequents.
Detective Clarence "Tango" Butler is an undercover cop working the drug beat. After losing himself in his role as a drug dealer, he is tired of the kind of attention that a black man in a black car attracts. Having been promised a promotion and a desk job for years, he is finally offered a way out by betraying a close friend Casanova "Caz" Phillips, a known criminal recently released from federal prison. Federal Agent Smith instructs Tango to set up the drug deal that will ensure the arrest of Caz and his return to federal prison.
Eddie's first rookie assignment is a former Marine, who becomes disgusted with Eddie's lack of professionalism and cynical outlook, and asks to be reassigned only to be killed on his next assignment. Eddie takes a liking to his second rookie assignment, who then accidentally fires his gun near a teenager during a petty theft investigation causing him to go deaf, leaving the NYPD facing a public relations nightmare. During the investigation, Eddie is remorseful for what happened, but refuses to play along with his superiors' attempts to imply that the teenager was a drug dealer.
When Tango goes to warn Caz to abort their upcoming drug deal, they are ambushed and Caz is shot, under orders from Red, a gangster Tango had humiliated previously. After Agent Smith makes a racist remark and refuses to pursue Red, Tango lunges at her, but is restrained by fellow officers.
Sal's latest raid on the complex was cancelled, but he decides to go to the location and rob the money he needs for his house. One of his team members, Detective Ronny Rosario, tries to stop him but fails. As he approaches the building, Sal passes Tango, who has come there to kill Red. Sal raids the apartment. After killing three people and finding their stockpile of cash, Sal is shot in the back and killed by a young man who became suspicious when he saw Sal enter the building. Tango gets his vengeance on Red, but is mistaken for a gangster and is shot by Rosario. Only after shooting Tango does Rosario realize he has shot another law officer. Rosario, still determined to stop Sal, is forced to continue his search for him. He witnesses the young man who shot Sal running away from the crime scene and is devastated when he finds Sal's body in the drug dealers' apartment.
Eddie retires and visits Chantal, who declines his offer to move to Connecticut. On his way home, Eddie sees a woman, who was reported missing, being shoved into a van. He follows the van to the Van Dyke housing projects, where he locates a sex slave dungeon in the basement. Eddie apprehends one of the men and is confronted by a second. Eddie tells the second man to get down, but is forced to shoot him in the chest, resulting in a violent fight that ends with Eddie strangling his opponent with a zip tie. Eddie finds redemption by rescuing the missing girls.

Question: Why Tango comes to appartment?
Answer: To kill red.