11 major unanswered questions after the Line of Duty season 6 finale

Here's what we're still pondering.

1. Is Chief Constable Osborne bent?

Right up until the Buckells reveal, Line of Duty season six was teasing us with the idea that Chief Constable Philip Osborne (Owen Teale) was going to be "H". And while it ended up being DCI Ian Buckells (Nigel Boyle) on the other side of that interview room, we're still not prepared to rule out the idea that Osborne is bent.

Firstly, as we saw in the finale, Buckells refused to answer AC-12's question about whether he and / or Osborne conspired to murder Gail Vella. On the one hand, he knew that lying could rule him out from witness protection; on the other hand, confessing could rule him out from immunity. But was he also protecting Osborne?

Then there's Osborne's determined anti-anticorruption crusade. He's in the process of merging three anticorruption units, while getting rid of troublesome Ted Hastings (Adrian Dunbar) and reducing staffing by 90 percent. Meanwhile, he's secured plum positions in anticorruption for his allies, including DCS Patricia Carmichael (Anna Maxwell Martin).

DI Steve Arnott (Martin Compston) told Carmichael he wanted to investigate the police officers who served on the deliberately-botched Lawrence Christopher case in 2003, one of whom was Osborne; in response, she told him that historic anticorruption cases were not a priority. Hmmm.

In a televised speech, the Chief Constable raged: "Let me be clear: these are the misdeeds of a few rotten apples. And to invoke institutionalised police corruption is an outrageous lie and an insult to my officers. The public don’t want police officers to be held to account for every little thing they’re meant to have done. They want us to get on with the job, and that’s what we will do.”

Perhaps he's simply concerned about the police force's PR, or he doesn't want to believe in police corruption because he's been in the institution for so long. But we still think he could be the rotten-est apple of them all.

2. Who killed Thurwell?

According to the Spanish police, the bodies found in Marcus Thurwell's house were absolutely, definitely the bodies of señor and señora Thurwell. They were strangled to death, and left to decompose for several weeks.

But why? Who did it?

Buckells didn't seem to be aware of Thurwell's death or the police raid on the house in Spain. If he had been, he might have stopped sending encrypted messages via Thurwell's communications devices in Spain, which were now compromised and in the hands of the police.

There's also no clear motive for killing him, or at least no motive that we know of. It's a mystery.

3. Why was Buckells freaked out by Jimmy Lakewell's murder?

When Jimmy Lakewell (Patrick Baladi) was returned to Blackthorn Prison after AC-12's disastrous attempt to spirit him away for an interview, he was led to a cell that already contained another prisoner: Buckells. And before the prison door slammed shut, fellow prisoner and OCG thug Lee Banks (Alastair Natkiel) jumped out from behind and strangled Lakewell to death.

This is what happens to rats, was the message from Lee Banks – while Buckells faux-casually tried to make tea, and sloshed the milk everywhere. He looked genuinely freaked out. This was one of the things that made us think Buckells was probably a bit of a bent copper, but not the top bent copper.

So what was really going on here? In the season six finale, it simply wasn't explained – but we can suggest three possible theories.

One: the OCG (or one of the many OCGs) was sending a message to Buckells, on their own initiative. This is plausible; we know that crime boss Tommy Hunter was the one calling the shots when he was alive, and even after his death the criminals have retained power, despite splintering into disparate gangs. The OCGs would have a lot to lose if Buckells cooperated with AC-12 in return for immunity or witness protection, and it makes sense that they'd send a message to him not to spill.

Two: Chief Constable Osborne was Buckells' co-conspirator in the Gail Vella murder (and other crimes), and he ordered the OCG to kill Jimmy Lakewell and put the fear into Buckells, reminding him to keep his mouth shut.

Three: Buckells ordered Jimmy Lakewell to be executed in front of him. But he's previously only ordered executions from afar; seeing murder up-close was unexpectedly upsetting, hence the shaky hand and the avoidance of eye contact.

Will we ever find out what exactly happened here? To be honest, probably not.

4. Why did Hastings spell it "definately"?

The "definately" misspelling was the key to bringing down Buckells, who repeatedly spelled "definitely" wrong in handwritten reports dating back to 2003. Chloe was able to match that up with the multiple uses of "definately" in the instant messages from "H".

But as fans will remember, there's someone else in the cast who has previously spelled "definitely" wrong. Back in season five, Ted Hastings went off-script when he was instant-messaging with the OCG (in the guise of "H"). It was the clue which made us really, really think he could actually be "H". And when he was asked about it in his interrogation, his explanation – that he'd been studying the spelling and syntax of "H" so he could mimic it – seemed quite implausible.

(While we're on it, we also never got a great explanation as to why Hastings took his laptop to a shop to be disposed of. Porn? We don't buy it, Ted.)

So what was that all about? It probably doesn't matter now – but still.

5. Is Carmichael ever going to do the right thing?

While Ted exhorted Carmichael to carry the flame of anticorruption, she seems to have zero plans of actually doing that. At least, not in any way that uncovers systemic, institutional corruption. Unless... she's playing the long game?

But Carmichael does now have a decision to make. Will she tell anyone about Ted's confession? And if so, will she do it because it's the right thing to do – or because she wants to hurt him, and stop his efforts to fight his enforced retirement?

6. Will Darren Hunter be brought to justice?

Darren Hunter, son of Tommy Hunter, is a nasty piece of work who (hopefully) is finally going to face prosecution for the murder of Lawrence Christopher. Or is he? Because, though DS Lomax (Perry Fitzpatrick) at Hillside Lane's MIT has brought him into the station and started an investigation, the cold case has yet to be officially reopened.

And Osborne has good reason to make sure it stays closed.

7. Is this the end for AC-12?

Honestly, it's not looking good. The merger of AC-3, AC-9 and AC-12 continues, and Carmichael's in charge – along with Osborne's other cronies. Ted Hastings has been forced into retirement, even though he's fighting it; and massive staff cuts are in the works.

Despite all this, DI Kate Fleming (Vicky McClure) has declared her intention to rejoin AC-12 (though Hastings is no longer around to nod that one through). And Steve seems to have decided to stay, too. Those may not be particularly great career decisions, but we wouldn't expect anything less of Hastings' best team.

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8. Does Buckells get immunity?

As we learned at the very end of the season seven finale, Central Police has submitted an application for public-interest immunity in legal proceedings against Buckells. If successful, no evidence relating to institutionalised corruption will be heard in court.

So does Buckells get immunity? Probably. As Buckells himself correctly pointed out, the big bosses in the police force have absolutely no desire to make any of this public.

9. How will the OCG and police network recover?

AC-12 might not have entirely destroyed the network of corrupt police officers and organised criminals, but they have at least put some major dents in it. Buckells is gone; so is PC Ryan Pilkington (Gregory Piper), who was the OCG's investment in the future. Thurwell is dead, too. And plenty of balaclava men are dead or in custody.

Plus, it could just keep getting worse. Thurwell and Buckells's laptops and communication equipment has been seized, and tech genius Amanda Yao (Rosa Escoda) is on the case – starting to track down end-user IP addresses, and working out who Buckells was in contact with. If Carmichael allows her to do her job, there could be quite a few more police officers called in for interrogation.

10. Who arranged the documents for Jo's prison transfer?

Somehow, someone mocked up a "production order" for Jo Davidson to attend an interview with the Murder Investigation Team (MIT) at Hillside Lane, forging signatures from both DS Lomax and DI Fleming. They then arranged for a prison van to take Jo over to the Hill, with corrupt prison officers Merchant and Leland aboard as well as another accomplice; en route, balaclava men were poised to hold the van at gunpoint so they could abduct and kill Jo.

Buckells suggested it was time for Jo to go. But presumably he didn't do all the admin and organisation for the prison transfer, so there must have been others working on this operation. That would include people within organised crime, but also – almost certainly – bent coppers within the police who knew all the systems and had access to the required forms. Maybe even someone within the MIT itself.

What was their ultimate plan, anyway? If Jo had been killed, it would have quickly emerged that the MIT was not expecting her for an interview, so the whole thing would have looked mightily suspicious. Or was this an attempt to frame Lomax and Kate? (If so, it would surely have failed, as both cops could easily make a case that the form was forged.)

Hopefully, all those end-user IP addresses will soon be identified, and a bunch more corrupt cops and criminals brought to justice.

11. Does Steve get together with Steph?

Steve told Kate that he has genuine feelings for Steph Corbett (Amy de Bruhn), and she seems interested too – leaving concerned voice messages checking he's OK. She's supportive of his addiction problems, and they both seem accepting of each other's physical limitations.

But Steve would have to keep some big secrets if he went out with Steph. Namely: the fact that he illegally searched her house and found the cash, and the knowledge that Ted Hastings got her husband John Corbett killed. Could a relationship succeed on a foundation like that?

Want more analysis of the finale? Take a look at all of the Line of Duty red herrings that teased and deceived the finale outcome.

Line of Duty season 6 is available on BBC iPlayer now. Check out the rest of our Drama coverage, or take a look at our TV Guide to find out what else is on.