So, tonight's the night we finally find out the truth about who was behind the police ambush that led to the death of witness protection officer Jane Akers and two other officers and why. We'll also discover who killed 15-year-old Carly Kirk. Is the same person responsible for both crimes, or are we dealing with something more complex than that? Here's our guide to the runners and riders:

DI Lindsay Denton

The case for: She took the fatal phone call to Akers. She was the only police officer to survive the ambush. DCC Mark Dryden, her former lover, has accused her of stalking him and there are hints she's playing a long game and setting him up. More than one person has described her as manipulative and an expert liar and she certainly has excellent research and planning skills. She has been shown to have a temper when pushed, which might put her in the frame for Carly if there are two killers and two cases.

The case against: She's the one who's been set up, Dryden having seen a way of getting rid of two problems at once by placing her at the crime scene. She's been tortured, imprisoned and generally put upon all series; even the moments when she fights back are generally driven by desperation. Yes, she covered up her abortion and that gives her a reason to hate Dryden, but it doesn't mean she's guilty of more than feeling satisfied at his downfall. Why investigate Carly's death if she's the killer? She clearly didn't know Manish Prasad or Jeremy Cole, which suggests she's telling the truth about the ambush.

The verdict: On balance I'd say more sinned against than sinning (and yes, she did love her cat).

DCC Mike Dryden

The case for: The first question you're told to ask with a murder is: who benefits? And in the case of Line of Duty it's hard to look further than DCC Mike Dryden. He had "sexual relations" with the 15-year-old Kirk, who subsequently turned up beaten to death and buried under a garage. He organised the switch on the night of the ambush, which put Denton on the rota. He gave the go-ahead for Denton to meet Akers on the night of the ambush. He lied about his relationship with Denton. He also lied about his wife's driving charge, either to cover up the fact she's an alcoholic (his line) or to give himself an alibi for the night of Carly's disappearance. Unlike Denton, he is clearly on close terms with Prasad. He may also be the corrupt cop referred to in Tommy's video rant. Prasad claims Dryden ordered the ambush.

The case against: Seemed genuinely shocked by the news of Carly's death. No real proof that he was in Tommy's back pocket. May well have been set up by either Denton or AN Mysterious Other.

The verdict: Definitely an old perv (DC Kate Fleming's term) with a cavalier attitude towards women both young and old. Probably not the actual killer.

DS Manish Prasad and DS Jeremy Cole

The case for: Most likely suspects for the ambush. Prasad recorded a dying declaration under duress from Denton claiming they carried it out under Dryden's orders. Cole all but admitted to at least murdering Georgia when he died, which means he was trying to kill Tommy. Prasad was described as Carly's boyfriend and also knows Dryden, thus he almost certainly introduced them. He removed Carly's DNA from her foster parents' house under false pretences and had links to the garage her body was found under. His computer had images of the dead girl and also of Dryden with Carly, suggesting he was planning a sideline in blackmail.

The case against: Prasad and Cole are clearly up to their necks in this. But is Dryden the man giving the orders? Given the way Prasad's statement was obtained by Denton, there's room for doubt.

The verdict: Guns for hire. The question is, whose?

DCS Lester Hargreaves

The case for: He hid the discovery of the tracker from AC-12 and clearly has an agenda. He spends a lot of time lurking and listening and doesn't seem terribly interested in either cracking his murder case or supporting Denton, even though he apparently believed she was innocent. If Dryden is being set up, why not by Hargreaves?

The case against: Just because a man's a lurker doesn't make him a criminal genius. No real evidence that he's involved in either case. Nothing to link him to Tommy.

The verdict: Les is ornery, certainly. But does that really make him a killer?

DS Matthew "Dot" Cottan

The case for: Was revealed in the first series as a corrupt cop who has been on Tommy's payroll since he was a kid. May well have wanted to silence Tommy when he no longer served a purpose. He's a consummate liar, so his anger about the ambush could just be a front. Could be acting on someone else's orders.

The case against: Could just be saving his own skin and making sure his dark deeds from season one don't come to light.

The verdict: With Dot, anything is possible. A lot depends on whether he's acting on his own initiative or serving a new (or old) master.

John Thomas "Tommy" Hunter

The case for: Talking of old masters – are we absolutely certain Tommy is dead? The law of television crime dramas says its not over till the dead body's carried away, and the shouty Scottish one is a hard man to pin down. We also have no real proof that the man murdered by Cole was actually Tommy: Denton never saw him, and Akers, who was apparently on the take, could well have switched her witness long before the cops arrived. It's possible that Tommy knew the ambush was coming and set his own decoy in place.

The case against: Tommy never struck me as smart enough to pull that sort of bait and switch off. If he did, for what purpose? And what does he have to do with Carly Kirk?

The verdict: 50/50. It's not implausible, but I'd be surprised.

Richard Akers

The case for: Jane Akers's husband was having an affair with Fleming but also knew about his wife's possible corruption. He may have decided to get rid of an inconvenient spouse and keep her dirty cash, but he may also have been in on the whole plot (whatever it is) and helped Jane set it up.

The case against: No real motive. No real opportunity. No real link to Carly Kirk.

The verdict: A leftfield bet but, as horseracing fans could tell you, they do sometimes come off.

DC Kate Fleming

The case for: Was having an affair with Richard Akers. Covered that up. Went after Denton with the zeal of the secretly guilty. Was the last person Akers phoned – why?

The case against: Having an affair doesn't make you a murderer.

The verdict: Guilty of bad judgment and lying to her family and colleagues, but probably not guilty of murder.

DS Steve Arnott

The case for: Slept with a key witness. Is possessed of a pair of eyebrows that can seemingly compel every woman he meets to jump into bed with him.

The case against: Has spent most of the series trying to uncover the truth, putting countless backs up along the way. These are not the actions of a guilty man.

The verdict: Having disturbingly magnetic eyebrows isn't really a crime.

Supt Ted Hastings

The case for: Has money problems, which leaves him open to blackmail. Desperate for promotion in order to win his wife back, which may have addled his judgment. Fudged Denton's case and failed to ask probing questions of Dryden.

The case against: Is one of the only characters on this show with anything resembling an actual moral code. Allowed his underlings to go ahead and ask the hard questions of Dryden even though it could destroy his career.

The verdict: If Ted Hastings is guilty there's no justice in the world and I'll eat my specially purchased set of clip-on ties.

Line of Duty concludes tonight on BBC2 at 9pm.

So who done it?

http://www.theguardian.com/tv-and-ra...d-it-bbc-drama