Zac Efron has spoken about how he got into the psyche of serial killer Ted Bundy at the premiere of his new film about the notorious US murderer.
The Hollywood star spoke to Sky News on the red carpet for Extremely Wicked, Shockingly Evil And Vile alongside his co-star Lily Collins, who plays his long-term girlfriend, Elizabeth Kloepfer (called Liz Kendall in the film).
After maintaining his innocence for years, Bundy finally confessed to the murders of more than 30 women and girls across several states in the 1970s before his execution in 1989. However, it is believed the real number of victims is still unknown and that the real number could be far higher.
For Efron, who is best known for films including the High School Musical series, The Greatest Showman and Hairspray, playing the infamous Bundy was a very different challenge.
"We had a plethora of footage, so much source footage from his different trials," he told Sky News. "There was a lot to go on.
"I worked on studying his mannerisms and all the classic stuff… There was a fine line between keeping it a real, honest character and doing an impersonation. It was a fair amount of work."
Handsome, intelligent and charismatic, Bundy was the monster hiding in plain sight; how could a man who was so charming, so good-looking, be capable of such evil?
That was how many saw him.
Rather than depicting the gruesome horrors of his crimes, the film tells the story from Liz's perspective, and is based on Ms Kloepfer's book, The Phantom Prince: My Life With Ted Bundy.
For years, she refused to believe he was guilty, and the film shows how easily the killer was able to manipulate those around him.
Collins, who met Ms Kloepfer as part of her research, told Sky News this was the reason she decided to take on the role.
"I wouldn't have signed on if it was a conventional slasher serial killer movie," she said. "It's too sensitive a subject matter with Liz being involved to do that. I think to pay tribute to her story it needed to be something different.
"It felt necessary to tell in that way, otherwise it was like telling the same story over and over again."
Director Joe Berlinger, who also produced the recent Netflix documentary series Conversations With A Killer: The Ted Bundy Tapes, said Efron took some "cajoling" to take on the part.
"He wanted to make sure we weren't just doing some gratuitous movie," he said.
"The reason I wanted Zac to play the role is that the lessons of Bundy can't be overstated. Bundy teaches us that the people who do evil in this world are the people you most often trust and who you least expect.
"To take that [Zac's] image and play with it in that way to me crystallises the intent of the film, which is to give the audience the experience of being deceived and betrayed by someone you know and love."
Berlinger said he wanted to take Efron's "real-life persona of a beloved heartthrob" and use it so that the audience "almost forgets" they're watching a film about Bundy.
The director said there had been "a million" serial killer movies where you see "an escalating body count and gruesome violence" but he had not seen one about "how serial killers function when they're not killing".
He continued: "That's an important aspect because we want to think a serial killer is some dark guy who's a social outcast, who doesn't fit into society because that gives us the false comfort that we can easily identify somebody who does evil.
"By telling the story from a victim's point of view, from somebody who believed in him, I think we're able to portray that phenomenon."
:: Extremely Wicked, Shockingly Evil And Vile is out in cinemas and on Sky Cinema from 3 May