Zac Efron enjoyed using his ''charisma'' as a way of ''manipulation'' in 'Extremely Wicked, Shockingly Evil and Vile'.

The 31-year-old actor portrays notorious American serial killer Ted Bundy in the upcoming biopic and admitted that although he was careful ''not to glamorise'' Bundy, he felt he could use his own good looks and charm to give the most ''honest'' performance he possibly could of the late murderer.

Speaking to BANG Showbiz at the European premiere of the film in London on Wednesday night (24.04.29), he said: ''I've never done a biopic before of this capacity and it's tricky it's like this genre you've got to be careful. You want to be as honest as possible, but not glamorise it.

''One of the things I felt like I could lend to playing Ted was that he was well known for his looks and for his charisma, I've been told in the past by some of the people here that I have charisma.

''I enjoy finding a way to use that as a way of manipulation, which is how it's honestly used in today's world. I think that people pull the wool over everyone's eyes all the time and I'm big on honesty that's why I love acting because it's honest.''

'The Greatest Showman' star went on to explain that he was ''conflicted'' playing Bundy - who committed numerous serious sexual assaults and murders on young women in the 1970s - and sought the help of his acting coach to discover more about his character.

He said: ''I was conflicted to play the character I had a lot of help Terry Knickerbocker my acting coach, who I'm not even ashamed to say I have.

''I love acting so I study all the time, we were able to figure it out and the question if a sociopath or a psychopath really does have three-dimensional capabilities of love and put ourselves in that era.''