SPOILER ALERT: this article contains details from the entire series of Making a Murderer on Netflix

Disturbed, devastated, depressed, confused, cynical, paranoid, spooked, hooked and dog-tired. That was how I felt crossing the finishing line of the true-crime marathon that is Making a Murderer. Our response to the story of a man accused of murder in the American midwest has been extreme and unprecedented. The past week alone has seen the film-makers defend their process on Newsnight; the White House issue a statement explaining why President Obama can’t pardon a state crime; and two middle-aged defence attorneys from Wisconsin become heart-throbs. Not bad for a low-budget documentary released on Netflix less than a month ago.

I will attempt to distil 10 brain-aching episodes into a single – spoiler-ridden – paragraph: in 2003, a 41-year-old man named Steven Avery was released from prison after serving 18 years for a rape he didn’t commit. The case was beset by accusations of police misconduct, and Avery was eventually exonerated using DNA evidence. But that’s just the first episode. Two years later, as Avery was about to sue authorities in Manitowoc county for millions of dollars, he was arrested again, this time for the murder of a local photographer, Teresa Halbach.

What follows is a dark, labyrinthine epic, stranger than anything previously branded “stranger than fiction”, and seemingly made to be binge-watched in winter on a streaming platform that wasn’t even commissioning original content when filming began.

Over a decade of filming – during which Avery was tried and sentenced to life imprisonment without parole – the show’s directors, Laura Ricciardi and Moira Demos, ended up moving to Wisconsin to be closer to the story as it unfolded. And what a story it turned out to be: a narrative with neither resolution nor end that leaves even the most fundamental question – who killed Halbach? – painfully unclear. Even its title, which at first sight is rather pedestrian, begins to widen in scope until it turns into another question: how is a murderer “made”? By bent cops, a flawed criminal justice system, a grossly unequal society, a bloodthirsty pre-trial publicity campaign or 18 years of wrongful imprisonment?

Steven Avery with his parents, who maintain his innocence. Photograph: Netflix

The questions keep on coming (and not just the ones from the actual series, such as: why was there a hole in that vial of blood?). Why has a long, slow, deep and at-times relentless documentary about a man accused of murder, and a police department of framing him, gripped the world? What are the implications of turning a real-life murder trial into a thriller as entertaining as any high-class HBO drama? Is it OK that 10 hours of telly have turned us into a global community of armchair detectives? Is it OK to be addicted to Making a Murderer? And, finally, why can’t I stop asking questions? (This last one may be a side-effect of binge-watching the series in two sittings, a condition characterised by an obsessive interest in advances in DNA testing and an inability to take anything at face value again.)

“I’ve never seen something that goes behind the scenes like this to see what it’s like to prepare for a serious trial,” says Jerry Buting, Avery’s defence lawyer. “That was the reason we agreed to participate in the first place. The public is given a sense of being jurors on this case; what would they do? That turns it into the ultimate reality show.”

The remarkable level of emotional investment in the story has crossed over into active participation, from a petition signed by more than 275,000 people calling on the White House to free Avery and his nephew Brendan Dassey (who lived next door and allegedly took part in the murder) to offers of help. Both Buting and Dean Strang, Avery’s other defence lawyer, have been getting hundreds of emails and calls from fans of the show. “It has been bigger than any of us anticipated,” Buting says. “There are people all over the world who are really picking this case apart now. And they are finding things that we just didn’t see.” Has it produced new leads? “Yes,” he replies tentatively. “We are investigating them. We’ve been contacted by scientists from all over the world with areas of expertise that may prove useful.”

Steven Avery’s defence attorney Dean Strang: ‘We had no idea what story they would choose to tell.’ Photograph: Milwaukee Journal Sentinel/TNS/Getty Images

What does Avery make of the response? “He has not seen the documentary,” Buting says, “but he is aware of it. People in their hundreds are writing to him. I think he is hopeful that something will come out of this.”

Strang tells me many “silk stocking” law firms have offered to defend Avery pro bono. The day after we speak, it is announced that Avery has new legal representation: a high-powered team led by top Chicago attorney Kathleen Zellner. The reaction to Making a Murderer, like that last year to the podcast Serial, goes way beyond entertainment. Could its influence actually lead to the case being reopened? “I hope so,” says Strang. “Maybe someone who saw something or has kept a secret for 10 years will come forward. And judges read online news sources just like everybody else. More broadly, I think the series will foster a larger conversation about the systemic weaknesses in the way we administer criminal justice. That would be a very good outcome of this documentary.”

As for the more unexpected outcome – becoming a sex symbol – he laughs it off, one suspects with a flick of his floppy hair. “It’s just silly. It’ll pass … I’m not on social media, but I’m hearing about it because friends are teasing me.” Strang, in particular, has been compared to Atticus Finch because of his compassion, decency and propensity to well up at the mere thought of injustice. “It’s very humbling,” he mumbles. “I can’t be Atticus Finch, so I have to satisfy myself by trying to be the best Dean Strang I can be.”

The show may have ended, but the story goes on. Last week, Ricciardi and Demos revealed one of the jurors in the trial had contacted them to say they believe Avery was framed. The pair have also been accused by state prosecutor Ken Kratz of leaving out of the film crucial evidence that points to Avery’s guilt. Some of these facts – for example, that Avery called Halbach three times on the day she went missing, twice from a withheld number to hide his identity – are deeply worrying and have blown my mind all over again. The film-makers have dismissed accusations of bias. “We took our cues from the state’s own case,” Demos insists. Ricciardi says: “We stand by the project we did. It is thorough. It is fair. That is why it took us 10 years to produce it.”

Brendan Dassey, Avery’s nephew, was also convicted of taking part in the killing of Teresa Halbach. Photograph: Eric Young/AP

What does Strang make of the allegations? “It’s a very unfair swipe at their integrity to suggest they turned editorial judgment on their film over to [the defence],” he says. “These two women gave Avery’s trial three hours of time. That’s more than is used in Doctor Zhivago to cover the entire Russian revolution. And I don’t think it’s fair when the criticism is coming from people who were repeatedly invited to co-operate and repeatedly said no.”

Why did he and Buting say yes? “Our client wanted us to consider participating,” he says. “We approached it warily, and over time it became clear that these were thoughtful film-makers who intended to raise broader questions about the criminal justice system. They were honest with us. They weren’t intrusive. They used one small camera and went away when we told them to. Trust was built up over time and they have never betrayed that trust. We had no idea what story they would choose to tell. I found out with everyone else when it became available in December and I sat down with my wife to watch it.”

Nevertheless, the world presented to us in Making a Murderer, whether by design or necessity, is largely from the perspective of the Avery family – who believe Avery is innocent. After all the signatures on petitions, theory-spinning on Reddit and offers of help, what if it turns out he is guilty? This is the deeply uncomfortable question casting a shadow over our appetite for armchair sleuthing. The implications of thinking we can make our own deductions and actually get involved are dark indeed when what we are talking about is a high-profile murder trial.

Making a Murderer represents the peak of a 21st-century trend in longform true crime. In a few weeks, it has seen a genre previously reserved for the likes of America’s Most Wanted or the Investigation Discovery network – widely seen as the home of low-rent, trashy true crime – cross over into mainstream and even highbrow culture. Ricky Gervais and Alec Baldwin have been tweeting about it. In many ways, Making a Murderer has done for true crime on television what Truman Capote’s In Cold Blood did for non-fiction in the 60s. “Our appetite for solving crimes goes back centuries, but it’s so much easier to access these stories now,” says clinical forensic psychologist Michael Berry. “In America, they’ve had TV in court for years. The whole case can be brought to you at home.” Documentaries such as Making a Murderer, in other words, are a natural progression in how we already consume true crime. “I remember, as a student, queuing up to go to murder trials in Birmingham at the crown court,” Berry says. “Now we are exposed to court cases in a completely live, blow-by-blow way.”

What links Making a Murderer with Serial, the HBO drama The Jinx and the BBC’s newly announced The Station is an ability to transform hundreds of hours (700, in this case) of complex, confusing and often tedious police procedural and courtroom testimony into short, sharp, addictive episodes with narrative arcs, shocking reveals and more red herrings than an Agatha Christie mystery. Immersive, demanding and often uncomfortably entertaining, these shows speak to our overstimulated and deeply cynical age. They are exhausting, yet we stream the next episode just the same.

The series was filmed over 10 years. Photograph: Danielle Ricciardi/Netflix

In the US in particular, Making a Murderer comes at a time of deep mistrust in law-enforcement officers and a perceived rise in shootings of unarmed victims. Last year, 1,134 people were killed by US police, with the rate of death for young black men five times higher than for white men of the same age. Making a Murderer reinforces what we already believe: that power structures are fallible and often corrupt. “What’s interesting is how some cases are picked up and others aren’t,” Berry says. “How did I guess that the two men involved in this case would be white?”

Making a Murderer shows us a US we recognise not only from the news, but also from popular culture, whether it’s CSI (once the most watched show across the globe, but cancelled last year) or Damages. It may have low production values, but there are more bleak aerial shots sweeping across a flat, rural, poverty-stricken midwestern county in Making a Murderer than you would find in a Coen brothers film (and one particularly oily lawyer who would be played perfectly by William H Macy). As Buting puts it: “People’s eyes have been opened in recent years. We now realise that a case like Steven Avery’s could happen to anybody.”

Perhaps the most remarkable aspect of the series is that, by the time it finishes, the question of guilt – that is, the one on which the trial, the futures of the Avery and Halbach families and an entire history of crime fiction rests – has almost entirely lost its force. Making a Murderer gives the whodunnit a postmodern shakeup and turns the question of Avery’s guilt on its head. In other words, the means become every bit as crucial as the end – and the means are screwed. This is why, for many, the most deep-rooted and devastating response to Making a Murderer is a loss of faith in the system.

Did this affect Avery’s attorneys, too? “It’s easy for people to become jaded, but I’ve tried not to,” Buting says. “I will say this, though: of all the cases, this was probably the most difficult one for me to disengage from once the trial was over. It took months. It was very hard to turn my attention to other cases.” He tells me he still struggles sometimes to sleep at night. “There are always things you wish you could have done differently. It still bothers me that we lost. I think about, for instance, whether it would have been better if Steven [had] testified. You could do that forever, I guess … you just have to push on.”

In one of Making a Murderer’s final and most moving scenes, Strang chokes up and says of his client, “I just hope he is guilty”, because the alternative is almost too much to bear. “That was a selfish comment I made,” he says. “I meant it, but I certainly don’t hope for Steven’s sake that he is guilty. It’s very hard to lose a case when the sentence is life imprisonment. And I don’t live in a state with the death penalty. I don’t have to confront the fact that if I’m the second-best lawyer in the courtroom they’re going to kill my client.” He sighs, and his voice begins to waver as it does so often in the documentary. “It’s hard to live comfortably knowing you lost a case and the consequence is that someone is going to await a slow death in prison. It’s unbearable if the person is innocent. We keep on, but the thought of that makes you quail and wonder if you can keep on doing it.”

Has the Avery case changed him? “It stands out,” he says eventually, “but it’s not alone. It’s in a handful of cases that are just … hard memories.”