US actor Scott Haze spent months in isolation and slept in caves to prepare for his role as a necrophiliac in James Franco's Child of God, which has premiered in Venice.
Based on Cormac McCarthy's novel of the same name, Haze stars as Lester Ballad, a violent man living on the fringes of society who descends to the level of a cave dweller and forges relationships the only way he can - by killing women and having sex with their bodies.
"Scott isolated himself for three months. He spent nights in caves and when he finally turned up he was transformed, and kept himself isolated for the whole shoot," said Franco, who described it as "a performance of a lifetime."
McCarthy's killer is based on real-life murderer and body snatcher from the 1950s, Ed Gein - who also inspired the films Psycho and Silence of the Lambs - and Haze said he had drawn on the Joker character from Batman for inspiration.
"It was hard being isolated, but I was driven by a sense of responsibility to McCarthy, to really capture the character's animalistic element," the 25-year-old said.
Franco said he had been inspired by Martin Scorsese's 1976 movie Taxi Driver.
"It was certainly a model for me, where you have a crazy guy at the centre but he is compelling and you want to follow him," he said.
"Usually with subject matter like this, it would fall into the horror genre. But this is not a thriller or a porn movie, it's a character study," he added.
Haze creates a character who disgusts but at the same time evokes pity from the viewer.
"Here's a killer that is bumbling, not so much a dark killer in the woods as a man who doesn't know what he's doing," Franco said.
Haze said: "Those around him in a way are even more violent."
The local police and villagers watch Ballard - who dresses up in women's clothes - with growing suspicion but make no attempt to approach him.
His desperation increases when he accidentally burns one of his precious corpses.
"Those around him become peeping toms, fascinated with this character," Franco said.
"There is a sort of underlying violence to everyone, it's just more ruled by the dictates of the law."