'With that first scene we could never ever have stones actually hitting full in the face from the front, that's just impossible to do. So we backed off a little from it; we saw the head twist back and did a lot with music and sound effects.' TV writer and crime novelist Hans Rosenfeldt is talking about the appalling scene which opened the fourth and final series of The Bridge when the general director of Copenhagen's Migration Agency is about to meet her end through a horrendous stoning.

This jaw dropping beginning was just one of many violent moments across 38 episodes of a show which was as dark as it was compelling. 'We want something to feel brutal, but never to have a shock effect purely for its own sake,' insists Rosenfeldt, one member of a writing team for the show which he created back in 2011. 'There are a lot of scenes on paper that are really disturbing but they're not over the border of what we can do. And in editing we can choose: "do we need this or should we take it away"?'

Rosenfeldt is rightly proud of the show's success, but he never dreamed that it would take off in the way it did with viewers outside of Sweden and Denmark (each series had storylines that brought the police forces of both countries together). The three cross-border remakes with cases traversing Russia and Estonia, the US and Mexico, and the UK with France (The Tunnel) held no real appeal to him though (neither presumably will the further two versions in the pipeline for Germany-Austria and Malaysia-Singapore). 'I watched a few episodes, but couldn't really enjoy them as a TV series. I job-watched them: "oh, they kept this, they changed that; oh, that's what they did there". It didn't give me any pleasure as a viewer so I stopped.'

Hans Rosenfeldt

Much of The Bridge audience's pleasure arrived through the interactions between autistic and talented detective Saga Norén (Sofia Helin) and her work colleagues, particularly the main sidekicks. She eventually helped put Martin Rohde (Kim Bodnia) behind bars at the end of series two after he gained vengeance on his son's killer, before developing a no-ties sexual relationship with Henrik Sabroe (Thure Lindhardt), a man tortured by the disappearance of his wife and two daughters several years before we first meet him in season three.

Plenty has been written and spoken, justifiably so, of the sensitive portrayal of Saga, but the forcible detail which went into writing other fully-rounded characters in the show should not be overlooked. 'Henrik is very likeable and a little bit more sad than Martin was,' states Rosenfeldt. 'We didn't replace Martin with just another Martin, we replaced him with someone who was equally or even more damaged than Saga is. Saga and Henrik needed each other very much and that's a good thing to play off.'

Although Rosenfeldt had a lot of fun working on a show which took up a substantial chunk of the last decade, he is convinced that ending The Bridge on a high was the correct decision. 'We were on public service channels and it's their duty to keep coming up with new stuff, new writers and new shows,' he notes. 'But it wasn't the broadcaster saying that this is the end, it was us saying it. We don't know too many shows that creatively peak at season six or seven, and we wanted to stop before people said "oh yeah, that used to be good".'

The Bridge season 4 and seasons 1–4 box set are released on DVD and Blu-ray by Arrow TV on Mon 2 Jul.