Kathleen Peterson's ill-fated fall down a set of stairs in 2001 was thoroughly investigated and is now considered a closed case, but Colin Firth said that playing her husband, Michael Peterson, in the HBO adaptation of The Staircase was one of the most perplexing roles of his life.
The actor told Vanity Fair it was "very, very hard" to know how to play the widower, saying, "I didn't always know how to orientate myself."
The questions surrounding this case forced Firth to find his own version of Michael, who is just as mysterious as the circumstances surrounding Kathleen's death. "I very much wanted to err toward finding my own interpretation," the actor explained. "That's partly because I don't really feel I have answers."
While Michael was convicted of first-degree murder in relation to Kathleen's death in 2004, he was later granted a re-trial. But after years of preparation, the author decided to enter an Alford plea in 2017, meaning he plead his innocence but acknowledged that there's enough evidence to be convicted. He was sentenced to 86 months in prison, with credit for the more than eight years he had already served.
And though Firth understood that answers would elude him, he shared that his cast members, including Sophie Turner and Parker Posey, were always coming up with their own theories. "It was fascinating just working with fellow actors and crew members, because I would hear people change their minds," he explained. "How hard it is to live with doubt, the preference to believe in something—it doesn't really make it true."
Because of the many theories that have emerged over the years, most of which were explored in the documentary of the same title, the producers decided that they'd have Toni Collette act out the ways Kathleen could've died. Collette said of the experience, "It's a very weird thing to have to do because, (a) it's horrible; (b) it really happened; and (c) these are all the things that people don't like to think about in life, actually coming to the fore—and I have to bring some honesty to it."
It was difficult for the actress for a number of reasons, as it required her to lean into her physical instincts. But showrunner Antonio Campos said that the re-creations were surprisingly believable, recalling, "The things you could never imagine that she does in the moment really surprise you—you go, oh, my God, maybe it was that. Or that. Or that must have been what it was like for her to be in that stairwell by herself."
Firth was impressed by the ease at which Collette portrayed Kathleen, saying, "I envy [Toni] tremendously as an actor because she has all the depth that could be required of an artist. She's got unlimited courage, but she can also do whatever you ask of her at the drop of a hat. I can't do that."
But Firth almost lost the chance to work with the Australian actress, because Collette worried about the ripple effects The Staircase could cause. She explained, "The one thing that perturbed me was the idea of bringing attention to someone who potentially did something very bad, fanning his flame yet again."
The thing that motivated Collette though was the fact that she could show Kathleen "as a person, prior to when she left her body," adding, "She had spunk and spirit, and she really lived and loved."
True crime fans can see how the cast brought this story to life when The Staircase premieres this spring on HBO.