CANNES • Before he made his new film about the death penalty, Boo Junfeng sat down to tea with some of Singapore's retired hangmen.

He also talked to the priests and imams who helped condemned prisoners make their last walk to the gallows. And, most difficult of all, he spent years trying to reach through the curtain of shame to families who had lost fathers and sons to the hangman's rope.

But it was only after Boo, whose film Apprentice premiered at the Cannes Film Festival yesterday, met one particularly "humane" executioner that he had an epiphany. He realised that no movie has ever dealt with the business from the perspective of the man who pulls the lever.

"I had started to write (the film), but after I met the first hangman, I couldn't write for three months. What threw me was how much I enjoyed his company," said Boo.

"He was not like I thought. He was likable, charismatic, grandfatherly, jocular and open about what he did. He took pride in the almost caring way he looked after the prisoners, trying to make it as humane as he could, and I realised how difficult that was. He really shook up my ideas and forced me to rethink everything."

So Boo, 32, took his film - which he toiled over for five years and which showed in the Un Certain Regard section at Cannes - one step further.

Apprentice has a shocking twist. It is the story of a young man who ended up learning the executioner's trade from the man who opened the trapdoor on his own father. More surprising still is the intensity of the almost father-son relationship that develops between the young prison guard and the hangman.

"He is in some ways searching for his father," Boo said. "And in doing that, he finds this man. What I was going for was human truth. I didn't want to make it an activist film."

Boo, whose semi-autobiographical first feature Sandcastle was a hit at the French festival in 2009, began his research with the book Once A Jolly Hangman, which features Darshan Singh, Singapore's chief executioner for nearly 50 years who once executed 18 men in one day.

Boo shot the prison scenes in disused prisons in Australia to avoid controversy in the tiny city state, where an estimated 95 per cent of the population still support the death penalty.

"Apprentice took so long because I had so much to learn, so many things were beyond my experience and very few people really knew (about this world)... And, unfortunately, almost all of them are not around" to tell the tale.

AGENCE FRANCE-PRESSE