The movie, which also stars Lily Collins as Liz Kloepfer (Bundy's girlfriend), just premiered at the Sundance Film Festival in Utah. While discussing the film, Efron said that he underwent "a rather large transformation and lifestyle change" in order to achieve a physique similar to that of Bundy.
"Guys in the '70s have that wiry, kind of thin look," the 31-year-old told Variety . "Ted was always kind of a little bit gaunt. He always looked pretty tired."
To shed weight, the actor turned to cycling and cardio exercises.
"I have a road bike that I ride around, well, everywhere," he explained to Variety . "I put that on a stationary trainer and every morning, I would get up and cycle on that for an hour and watch something episodic like 'Ozark.' I wasn't eating carbs. I kind of just trimmed down a lot and really controlled my diet."
Efron added that he spent approximately two weeks in an abandoned prison, which is also where he filmed a nude scene for the film. In addition, he wore fake teeth to look even more similar to Bundy, who confessed to murdering 30 women across several states.
"Our top teeth were very similar," he told Variety . "I had a lot of similarities with Ted that were a little bit unnerving."
"Extremely Wicked, Shockingly Evil and Vile" tells Bundy's story primarily through the lens of Kloepfer, so Efron and Collins spoke with people who knew Bundy prior to his execution in January 1989. The "Baywatch" star also watched real-life footage of Bundy during his trials.
"Something clicked pretty early on, and it was kind of scary," Efron told Variety . "It was that Ted and I had quite a bit in common in the way we carried ourselves. There are a few mannerisms. You can tell he's a bit bashful. He's kind of shy. He's a well-spoken guy, but he hides his anxiety with a bit of a smile. I didn't want to do too much of an impersonation."
Since the trailer was released, many people have criticized the film of glorifying and romanticizing a brutal murderer. According to Efron, "Extremely Wicked, Shockingly Evil and Vile" will look at Bundy from a psychological perspective.
"I feel a responsibility to make sure that this movie is not a celebration of Ted Bundy," Efron told Variety. "Or a glorification of him. But, definitely, a psychological study of who this person was. In that, there's honesty."
