Capital punishment is dehumanising. That was the topic of a debate film-maker Boo Junfeng took part in as a student at Chung Cheng High School.

"I didn't even understand what dehumanising meant. Even with the definition in the dictionary, it felt a bit abstract," he says, recalling that he was on the team proposing the motion.

"I remember losing the debate," he adds with a laugh.

The research he did on the topic - lethal injection, electric chair, wrongful convictions - stayed with him. "When I became older, when my world view broadened and I understood things more deeply, that's when I started to take notice of the discussions that were happening here."

His second feature, Apprentice, is about a young prison officer, Aiman (Fir Rahman), who gets taken under the wing of prison executioner Rahim (Wan Hanafi Su).

Aiman's sister, Suhaila (Mastura Ahmad), frowns on the apprenticeship of her brother, who has personal reasons for wanting to get closer to the executioner.

The film, which premiered last month at the prestigious Cannes Film Festival in the Un Certain Regard section, opens here tomorrow.

While Boo, 32, is personally against the death penalty, which is carried out in Singapore, he is wary of having Apprentice seen as an issues movie.

The soft-spoken film-maker, whose debut feature Sandcastle (2010) dug into the once-taboo topic of leftist Chinese student activism in the 1950s, says: "Sometimes, topics may seem contentious and difficult to deal with, but I've always believed that through story- telling, through film, when we are able to humanise characters and make them relatable, these topics no longer remain just topics.

"They become human experiences with the potential of inspiring empathy. The world could use a bit more empathy."

The desire to come up with flesh- and-blood characters meant that the writing process took time.

Describing an early draft of Rahim as "essentially a caricature", Boo says: "In order for the story to work, since I was trying to explore the human psyche of this profession, I needed to understand this character as a human being."

So he put the word out through friends and eventually managed to speak to two retired executioners. While he already had a specific character in mind, one with motivations and principles, "meeting these two men helped me humanise" the role.

He even had afternoon tea with one of them and his family at his home and realised "they are no different from any everyday uncle", and that helped him to see Rahim as a person who is relatable.

Apprentice, rated M18 in Singapore, has an ending which is left open to interpretation.

But Boo says he was not under pressure to nudge the film in a certain direction despite the thorny subject of capital punishment.

"The way the film ends was in my very first pitch to my producer. Three years of writing and developing and another year of editing the film were all working towards being able to end the film this way.

"It needs to be thrown back at the audience, for people to contemplate it a little further."

The feedback he has received so far has been positive: "People have told me that the film stays with them."

Casting was also a key process and it took about a year. A little unusually, he wrote the characters without specific ethnicities in mind and held colour-blind auditions.

"It didn't matter so much what the actors' race was going to be and what language they were going to speak. For me, what was more important was widening the talent pool."

And so he reached out to anyone who was of the right age and physique, regardless of whether they were professional or nonprofessional actors.

He had a lucky break when it came to Malaysian actor Wan Hanafi. Boo had picked up a bunch of films from a DVD shop in Kuala Lumpur and binge-watched them in a hotel.

The movies included the thriller, Bunohan (2012), by director Dain Said. "I saw this beautiful-looking old man with white long hair and I was like, 'Him! Who is he?'

"What I really liked about Wan Hanafi was how unpredictable he was and, at the same time, the gravitas he naturally had has helped to anchor the film."

As for Fir, he was just starting out then and has since become more known on Suria channel and in the theatre scene.

Boo says of him: "There was something very quietly intense about him that I felt was very suitable for Aiman."

The chemistry between Wan Hanafi and Fir worked as well. Boo points out that their characters naturally speak in Malay and so he roped in home-grown playwright- director Irfan Kasban to work on the translation of the script.

Apprentice jail scenes shot in Australia

He and Irfan, whose work Trees, A Crowd... was recently presented at The Twenty-Something Theatre Festival, had worked together in an artwork by Boo titled Mirror, which won the President's Young Talents award in 2013.

While Boo was a little apprehensive at first about the Malay dialogue, given that he does not speak the language, he found out that the intonations were familiar, thanks to similarities in Singlish.

Irfan also served as interpreter and language consultant on the set.

The bigger challenge was that the scale of Apprentice is much larger than that of the family drama Sandcastle.

Filming was done on location in New South Wales, Australia, at two decommissioned prisons - Maitland Gaol and Parramatta Correctional Centre.

The jail in Apprentice is not just a physical space, it is also a psychological space where "Aiman is embarking on a journey to himself".

Something "old and historic would have made a lot of sense for the characterisation of the prison" and Boo could not find a suitable location in Singapore.

Shooting overseas was a decision that had to be made quite early on as it meant the budget for the project had to accommodate the added expenses.

The film is a co-production involving Singapore, Germany, France, Hong Kong and Qatar. Its budget of $1.8 million is partly funded by the Media Development Authority, including under its Development Assistance (up to $40,000) and Production Assistance (up to 40 per cent of a project's qualifying expenses) schemes.

A sequence in the film might have the actors walking across an office in Ayer Rajah, through a corridor in a location in Beach Road, out into an armoury in Parramatta, into the yard at Maitland and to the gallows, which is a set in Singapore.

Boo paid much attention to how the disparate locations could be stitched together to form a single coherent space, for example, through the use of a unifying colour scheme. He did it so well that when he described the film's screening as a homecoming of sorts at the recent Sydney Film Festival, audiences there were surprised.

His hope is for as many people to watch the film as possible and that there will be strong word-of-mouth for it.

Apprentice is being released in Singapore now to ride on the publicity from Cannes, but he acknowledges the tough competition it faces from summer blockbusters such as Finding Dory and Independence Day: Resurgence.

Boo, a graduate of Ngee Ann Polytechnic and The Puttnam School of Film at the Lasalle College of the Arts, has been feted for his short films since 2004's A Family Portrait as well as for Sandcastle, which premiered at Cannes at International Critics' Week.

He has a clear-eyed view of festivals and awards.

"These things are never guaranteed. Sometimes, the factors that go into a film being selected or awarded go beyond the merits of the film. We can only hope we get this recognition and that that encourages the public to come and watch the film."

His humanist perspective and willingness to engage with sometimes controversial issues are qualities that distinguish him as a film-maker and those seem unlikely to change.

Boo, who is in a relationship, says: "I will continue to make films with themes that matter to me. I found it very interesting to be working with big themes, but making them personal and intimate. That's one of the most important things about making the films I make."

•Apprentice opens here tomorrow. Director Boo Junfeng will appear at the Blog Aloud: Apprentice screening at GV Plaza tomorrow at 6.45pm. Tickets at $15 are available at www.gv.com.sg