Informer series ending explained | will there be a second season? BBC drama writers talk us through that final episode. Also ABC in Australia

And now finally we know who fired that gun: Nasir Shar.

So what was the thinking behind this dramatic ending? Writers Sohrab Noshirvani and Rory Haines answer RadioTimes.com's biggest questions...

1. Why did Nasir have to be the shooter?

Reiss Jeram plays Nasir Shar in Informer

"It's really a calamitous tragedy in its own way, how it all unfolds," says Noshirvani. "Sometimes we think there's a clear plan, and it's all coherent and someone had a plot – which is sort of why we called the episode The Masterplan, because there is none. It's complete chaos that results in this."

Raza's little brother, played by Reiss Jeram, has always been at the periphery of the story. A smart and witty teenager with a talent for photography, he was left to his own devices while Raza (Nabhaan Rizwan) disappeared into his secret work as a police informer. Disaster struck when he was befriended by Bridge Town Estate's angry troublemaker (and Islamic extremist keyboard warrior) Akash Williams (Kaine Zajaz).

Naive and impressionable, he began to emulate his new friend. Simultaneously, his family was falling apart around him: a father with a drinking problem, an absent brother, a terrifying police raid.

So when he accidentally shot Akash while trying to wrestle Dadir's old discarded gun out of his hands, Nasir was desperate and panic-stricken. He thought he had killed his friend, and – thanks to a bystander's footage and irresponsible online reports – he thought his own brother had been involved in a terror cell.

Wandering the streets of London with the gun in his pocket, he happened to lock eyes with Holly through a café window – and saw red: here was the policewoman who had kicked off the destruction of his family, from the very first moment she had appeared at his front door.

He shot again and again, before turning the gun on himself.

"With Nasir I think if you go and watch the season from his perspective, a lot of the signs of a young man in trouble are there, and are caused by the central plot," Haines explains.

"But of course we're not really looking at that. And neither is Raza and neither is Gabe, they're focused on what's ahead of them which is the more demanding storyline, of their work for CTSU and hunting the suspected terror cell."

Noshirvani adds: "Part of the point of the story is how violence begets violence. Oftentimes when we talk about radicalisation, we talk about ideology, but we never talk about violence."

The screenwriter explains: "Nasir is seeing his family torn apart, he's seeing the police knock down his door, and there's no one there paying attention to guide him away from that violence. And the one voice in his ear is Akash, who is not necessarily a very good role model for him in this situation."

Informer gives us an extremely sad ending for the Shar family, a bitter postscript that Noshirvani describes as "the sting in the tail of our story." With Nasir dead and his life in tatters, Raza has covered the wall of their shared bedroom with his little brother's photographs; in the family flat, his father Hanif Shar (Paul Tylak) lives with abusive graffiti scrawled over the boarded-up windows.

And, most heartbreakingly, his "Amma" (Sunetra Sarker) – the woman who raised Raza and Nasir after their mother's death, and the woman he sacrificed so much for in order to get her a British passport – has left everything behind to begin a new life, telling Raza that Nasir "wasn't even my son." Ouch.

But Haines and Noshirvani say the story had to end this way.

"We researched this subject matter for a long time, and it felt false to give a very happy ending to this story," Noshirvani tells us. "It's really about: a tragedy happens, how did we reach this tragedy?"

2. Why does Raza become "Clover"?

Over the course of six episodes, Raza's life has been completely shattered. He can never truly go back to being a civilian – which is why we see Gabe handing him an envelope with his new code name, "Clover", as he slips into the seat behind him on the DLR. Their relationship isn't over yet.

In fact, despite the way Gabe has used and abused him, the connection between handler and informer has never been stronger.

"He's really under Gabe's spell at that point – more so than at any other point," says Noshirvani. At this point Gabe is the only one who he can properly talk to.

Haines adds: "We found from our research that people who live these kinds of duplicitous double lives really, really rely on the handlers emotionally, not just strategically, but emotionally because they're the only people who know both sides of them.

"And for better or worse, Gabe is the one person who knows what Raza's going through and has been through."

3. Why does Holly's sister tell Emily about "Charlie"?

Bel Powley plays DC Holly Morten in Informer

Because she's angry – and because she knows that both Gabe (Paddy Considine) and Emily (Jessica Raine) are connected in some way to Holly's untimely death.

"We tried to look at it from everybody's perspective and she also doesn't know any of the things, she doesn't know what's gone on, you know?" Haines says.

"She has a limited knowledge and I think when you experience a tragedy first hand and you don't know all the pieces, it can lead to a lot of bitterness.

"She knows that there are lies that are being told to the public, she doesn't necessarily understand what those lies are for or what's behind them, but she knows that something happened to her sister that she doesn't fully have a grasp on, and so that's why she's lashing out – and Emily is the one person that she can approach."

4. Will there be a second series of Informer?

"I will say that when we first came up with this story, we imagined it as more than one series," Noshirvani tells RadioTimes.com. And any future series would focus again on the relationship between Gabe and Raza, handler and informer.

"Their relationship has always been the crux of the show for us," the screenwriter explains. "It's not necessarily about counter terror in that way... it's not really about that, it's about their relationship in the end.

"And so we've kind of just gotten them to a point in their relationship where it's really getting really interesting for us, the power balances can really shift."

"Certainly for Raza it doesn't feel for us like an end," Haines adds. "He's still a young man with lots ahead of him, who's going to have to come to terms with a lot of this."

There's also the relationship between Gabe and Emily, especially after Holly's sister hinted at some of the things Gabe had said the night before the shooting. Things which Holly never got to tell Emily before Nasir burst in with the gun.

"We didn't want to just forget about that storyline, because it's not something that Gabe can just shed after one confrontation with Holly," Noshirvani explains. "It's not like that story's over."