Perez is adamant that Turk is the murderer, and with the fact that since the beginning of the movie we're watcing him confess to the murders on camera to a panel of FBI agents, the case looks fairly open-shut on this one.
Things start to unravel when a giant Rusky is shot several times, but still survives. The way he says "Detective?" is what did it for me, and from that point it was obvious what was going to happen. Anyway, in hospital he wakes up from his coma but his heartbeat goes through the roof when he sees Fisk (Pacino) in the room. Ding ding.
Someone we assume to be Turk goes to the hospital to kill the Russian but is stopped in time by a cop on duty. Unable to finish the job he just leaves the room.
In a little while, Karen returns to her apartment where she is snatched again (like in the earlier scene) but then beaten and raped. She screams at the man as he leaves. She phones the department demanding action, and then takes it on herself to do something about it.
Perez and his partner organise a sting using 50 Cent to call Turk to the bank-club where they hope he'll leave a poem and try to kill the drug-dealer. The only poem he has is about how weak the trap was. The two other cops give up and hit the street to find the real murderer. Meanwhile Karen goes straight to the hospital, and shows a hidden picture to the Russian asking if that is the man who shot him. The Russian nods.
Spider phones his girl, and Fisk walks up to him calmly and shoots his brains (and his body) out a top floor window.
Turk is in shock. Fisk asks him to read from his diary to the security camera, to explain why he started the killing spree. Turk chases his friend, Karen gets in the way, then Turk traps Fisk in the linen warehouse. They talk some more, Fisk raises his gun and Turk shoots him in the chest. He calls it in but then cancels the ambulance so his friend can die.
The Feds watching the video agree to close the case. A little in the future, Turk is back coaching the girls softball team watched by Karen.