SINGAPORE - You might say that Shirkers is a documentary that took 25 years to make.

Sandi Tan, the former Straits Times film critic and novelist who now lives in Pasadena, California, made a movie with her friends in 1992. She was 19 then.

If it had been released as planned, it might have been the first movie of Singapore's 1990s local film renaissance, beating Eric Khoo's first feature, Mee Pok Man (1995).

Helping her and her friends Jasmine Ng and Sophie Siddique was an American mentor, the school teacher Georges Cardona. He directed the movie about a young assassin, played by Tan, who can kill with a finger gesture. It was titled Shirkers.

It was all going well until Cardona, whom Tan at the time thought was her best friend, disappeared with the 16mm film reels. Tan went on to work as a film critic for The Straits Times before going to Columbia University's film school. Later, she penned the epic novel The Black Isle (2012).

Then a few years ago, Cardona's widow sent boxes of his things to Tan's Pasadena home and in them was the long-lost film, perfectly preserved but without sound. The audio tracks, recorded separately, are still missing.

Using the material she found to put a proposal together, she was accepted in the 2016 Sundance Documentary Fellows programme. There, she managed to find grants to make Shirkers, the documentary about three film-loving teens, their strange American mentor and the long, winding journey the reels took to her home, where she lives with husband, film critic John Powers.

The film contains footage the group shot in 1992, and interviews conducted in 2015 with Ng and Siddique.

Tan on Sunday (Singapore time) won the World Cinema Documentary Directing Award for Shirkers, making her the second Singapore-born film-maker after Kirsten Tan (Pop Aye, 2017) to win an award at the festival.

Reviewers have praised Shirkers the documentary. Sheri Linden of The Hollywood Reporter calls it "a wry and wistful portrait of the artist as a young punk... she's fashioned a crime-of-the-heart investigation that has a gumshoe pulse and casts a hypnotic spell".

Indiewire's Eric Kohn says the documentary has "the handmade delicacy of a scrapbook come to life".

The Guardian's Charlie Phillips gave the film a full five stars, calling it "a joyous and funny recollection of a youth when anything felt possible".