Aged 102, Bi Kidude, the gravel-voiced singer known her raucous sense of humour and her love of cigarettes, suddenly vanished from her home.

Amid an explosion of intrigue and speculation, friends and fans on the island of Zanzibar, where she had lived all her life, scrabbled to find out what had happened to this doyenne of East African taraab music, who had become a national treasure and leading exponent of contemporary Swahili culture.

Then, a couple of days later, an unknown man claiming to be her nephew popped up on national TV. He said he had kidnapped her to protect her from “being exploited” by her musical collaborators, and that he would stop her from ever performing again.

The frantic search for Kidude is now the subject of a new documentary which explores her remarkable life story, spanning humble beginnings in the N’gambo slums in Zanzibar through to sellout performances across the globe.

Maryam Hamdani, one of Kidude’s oldest friends and partly responsible for her re-discovery in the 1980s recalls: “The first time I saw her was maybe 1985 or 1986. Everyone made fun of her because of the way she was singing and the way she was dressed. But I admired the way she sang and thought this woman has a golden voice but nobody sees it.”

Under Hamdani’s tutelage, Kidude joined Mohammed Ilyas and the Twinkling Stars as their lead singer, and her career enjoyed a staggering upturn, with international audiences transfixed by her fearless performance style.

Her sudden fame led to countless awards, including the 2005 Womex world music prize, which saw her hailed as “a cultural mediator and advisor of the younger generations… a proper symbol of world music’s emancipatory, liberating and strengthening power.”

But according to Yusuf Mahmoud, her de facto manager, it wasn’t until later “that Zanzibar finally woke up to the fact that this treasure was on the island.”

This awakening brought its own difficulties. Mahmoud remembers meeting Kidude at her home in Stone Town, Zanzibar’s capital, in 2004. “She had $3-4,000 [on her person], and lots of people came knocking on her door with lots of emergencies that needed to be addressed. Within ten days, she was penniless.”

Film-maker Andy Jones, who first made a documentary about Kidude in 2006, had lost contact with the singer when, in 2012, he was contacted by friends on the island who told him of her disappearance.

He immediately picked up his camera and returned to Zanzibar to document the search to find her. The resulting film, I Shot Bi Kidude, follows the trail of her kidnapper, eventually leading to a man called Baraka, her “nephew”, who had been keeping Kidude hostage in a house where she was clearly in a state of distress.

Though the veracity of Baraka’s claims of financial exploitation and abuse are never entirely clarified in the film, it’s clear that Kidude had, in her old age, been sucked into a murky world of hangers-on, who had looked to her for financial help.

Amid the whispers of exploitation, one thing shines clear: music was Kidude’s lifeblood. A poignant declaration, made during one of her final interviews, proved prophetic: “Music is my life. If I stop singing, how do they expect me to survive?”

She died just a few months later.

I Shot Bi Kidude is screening as part of the East End film festival on the 3 July