At 1.30pm on Friday 8 July, Kimonti Carter will learn whether he must spend the rest of his life in prison – or if American justice allows for the possibility of redemption.

Carter was riding in a car with fellow gang members in 1997. One told him to shoot at a car in the next lane, mistakenly believing that it belonged to a rival gang. Carter fired several shots, killing Corey Pittman and injuring two other passengers.

Just over 18, he was tried as an adult, convicted of aggravated first-degree murder and sentenced to 777 years, 77 months and 77 days’ imprisonment. Since Washington state has no parole system, it effectively locked him up and threw away the key.

But instead of yielding to hopelessness, Carter has dedicated his life behind bars to working as a teacher, mentor and founder of a groundbreaking prisoner-led higher-education programme. At a resentencing hearing at Pierce county superior court in Tacoma, Washington, on 8 July, he will ask to be set free.

“He never thought he was getting out and so he decided to make the most of his grieving by doing something so he can prevent things from happening,” says Gilda Sheppard, who interviewed Carter for her documentary, Since I Been Down. “There’s always a possibility of change. I have to think that.”

Filmed over 12 years, Since I Been Down paints a stark portrait of a predominantly white state, Washington, whose prison population is overwhelmingly Black. It shows Tacoma, near Seattle, as scarred by drugs and lack of investment in housing, education and employment. With opportunities scarce, gangs offer a seductive sense of identity. One former gang member recalls: “I got addicted to being feared.”

Sheppard, who teaches at a liberal arts college in Tacoma, says: “It’s like Everytown USA. It has been a victim of gentrification, a legacy of people not being able to have bank loans, or any kind of loans, to rehabilitate their homes. As a result, these neighbourhoods become infested with public health issues. Disinvestment in communities and education and employment comes with gentrification.”

In 1993 Washington became the first state in the US to pass a “three strikes” policy, which mandates life in prison without parole for people thrice convicted of certain offences, from robbery to assault to murder. The consequences were devastating for a generation. By the end of 2020, Black people, representing 4% of the state’s population, accounted for 38% of those sentenced under the law.

Speaking via Zoom from her home in Seattle, Sheppard reflects: “It’s not just the three strikes and you’re out but a culture of punishment that you see in many different urban communities, particularly Black, brown and poor communities. Tacoma, Washington, is a visual metaphor for the legacy of those things.”

This was the era of moral panic and so-called “tough on crime” policies across America that targeted Black “super-predators”, including three-strikes laws that sent young people to prison for life. President Bill Clinton signed a national crime bill now widely blamed for giving the US the highest incarceration rate in the world.

Mary Flowers, an anti-racism organiser, says in the film: “This country is based on fear. When you have a country that is based on or has grown out of colonisation and slavery, people don’t rest easy. That’s why everyone needs to be armed in this country to protect what they have, because what they have was stolen.”

But this is also a documentary about resistance and reinvention. For more than a decade Sheppard has been teaching sociology classes in Washington state prisons through the Black Prisoners’ Caucus, which started half a century ago and is now in a dozen prisons across Washington. She was surprised by the inmates’ academic discipline and engagement.

“I taught this concept of sociological imagination that looks at a person’s biography and how history informs that biography,” Sheppard recalls. “I was getting all this brilliant analysis and I was like, ‘I’m supposed to impart this. You all know this! Where’s the scaffold for this political and creative thinking?’

“So then I went to a summit of the Black Prisoners’ Caucus talking about youth violence, legislative process; they brought representatives, senators, the head of the department of corrections, some victims that could and other people in the community, their families, and I thought to myself, as James Baldwin said, to be an artist is to be a lover.

“If I love you, I have to show you things that you don’t see. I didn’t see this and I dare say I’m not sure a lot of people saw who we are imprisoning in our culture of punishment, even with the triumphs and redemptive possibilities of these men and women in prison. I just wanted to share that in my art.”

In 2013 Carter and the caucus created a programme called Taking Education and Creating History (Teach) in which prisoners teach literacy, maths and language courses to one another. It includes white inmates and is now at three Washington prisons. Carter now teaches algebra, financial literacy, interpersonal communication and African studies.

Sheppard witnessed how the initiative gives incarcerated people a sense of purpose, self-possession and hope. “When you meet one member of a community that has been shut off and wants to maintain those views of fear and hate and all those things, but that one member of that community gets a little bit of light, it’s hard to stop that light from shining. I’m not talking about optimism. I’m talking about real work.”

She was particularly struck by a “healthy thinking” class “to understand that to have education is not enough. What is your perspective? Who are you looking at as the good guys and the bad guys? Does history repeat itself or do people repeat history?

“In those classes I heard from different incarcerated folks from their heart and soul about their families, how they could cry together, going deep into remorse. One guy said his son wanted to come to prison so he could be with him. Or there’s one white guy who says, ‘I got seven kids. I don’t want to be like this. I want to change the way I’m thinking,’ Oftentimes prison is not a place where you can reflect. But these prisoner-initiated programmes realise what is needed in a person’s life and oftentimes they would invite some of the staff.

“When they go and hear these guys talking, they can’t help but listen a little bit. I am not naive to think that everybody’s going to change, but maybe a member of that community has something else that they haven’t looked at, and who knows what they can do?”

Carter, a leader in the Black Prisoners’ Caucus, emerges as the documentary’s central protagonist. Sheppard came to admire his “compassionate leadership and vision”, she says. “He would look at situations, but also imagine what was possible, hence his development of Teach across race lines. He’s remorseful but his remorse is not in a kind of grieving that’s only filled with tears but a kind of grieving that’s filled with activity.

“Just the other day, my film was shown at a juvenile facility, Green Hill school – young men between the ages of 16 and twentysomething – and they were very quiet afterwards. Kimonti Carter calls in sometimes when I’m doing these post-screening discussions and it was the most amazing discussion you could ever hear. He’s devoted his life to this.”

In 2006 Carter spoke at the Black Prisoners’ Caucus justice reform summit, apologising to the family of Pittman and taking responsibility for his crime. His life sentence was based on arbitrary legal technicalities. If he had been on the street instead of inside a moving vehicle at the moment he opened fire, or if he had been just six weeks younger when he committed the crime, he would probably now be a free man.

Yet the lack of a parole option meant he was told that, irrespective of how he behaved in prison, he would never be released. Sheppard reflects: “You’ve been held accountable. You did the time. But not only did you do the time, you helped to redeem so many other people who were in prison, across race lines.”

Carter’s sentence was finally vacated after the Washington supreme court ruled that mandatory life sentences without parole are unconstitutional for people aged 18 to 21, not just those under 18. At his hearing on 8 July, Carter will ask a judge to resentence him to “time served”, amounting to the 25 years that he has been imprisoned already. This would allow the 43-year-old to be released immediately.

In one scene of the film, Carter is seen hosting a caucus meeting. Wearing white T-shirt and beige trousers, with pen behind ear and notebook in hand, he tells fellow inmates: “Not only do you have to make a commitment but you have to make a choice: if I still want to continue living the life that got me here or I want to try to live a better life, right? We can never become somebody different but we can become a better version of who we are.”

• Since I Been Down is now available on Sundance Now or to rent digitally in the US with a UK date to be announced