This story of a miscarriage of justice is told with enormous sensitivity, intelligence and insight by documentary-makers Julie Ha and Eugene Yi. Their subject is Chol Soo Lee, who was falsely accused of murder in 1973 aged 20 and served 10 years in prison, four on death row. His case sparked a social justice movement that brought together long-haired hippy students, patent-leather-handbag carrying pensioners from California’s Korean churches and the wider Asian American community.

Lee was accused of killing Yip Yee Tak, a gang leader shot dead in San Francisco’s Chinatown. He was arrested after some spectacularly numbnuts copwork (officers initially described Lee as Chinese American; he was born in Korea). The whole of Chinatown seemed to know the police had the wrong man; nevertheless, Lee was convicted on the eyewitness testimony of white tourists. His case became a cause after reporting by the wonderfully charismatic Korean-American investigative journalist KW Lee.

Chol Soo Lee died in 2014, but we hear from him in extracts from his memoir (voiced by Sebastian Yoon): he describes being brutalised in gang-ridden San Quentin, where he was convicted of a second murder after killing another prisoner, described in the film as a neo-Nazi. Lee claimed self-defence.

What makes the film so engrossing is how much attention the film-makers give to Lee’s complicated life after prison; he was acquitted in a retrial of Yip Yee Tak’s murder and released in 1983. Lee wanted a happy ending – to lead a good life, make his community and supporters proud. But he struggled to adjust, battling demons and addiction. It’s a desperately sad story. Incidentally, in 1989 Hollywood made a drama inspired by Lee’s retrial called True Believer. There’s a clip here that shows his defence lawyer (played by James Woods) as a white saviour swooping in to save the day. It’s good to see that error corrected.

• Free Chol Soo Lee is released on 19 August in cinemas.