'The Staircase' Series Casts Toni Collette As Kathleen Peterson

The Staircase has found its Kathleen Peterson in Toni Collette. Collette joins Colin Firth in the HBO Max limited series, which is based on the true crime docuseries of the same name. The series tells the story of Michael Peterson, who was convicted of murdering his wife Kathleen. Peterson's defense team argued that Kathleen's death was an accident caused when she fell down a narrow, dark staircase in the couple's home.

Deadline is reporting that Toni Collette is joining The Staircase cast as Kathleen Peterson. While Kathleen is already dead when The Staircase docuseries begins, it's likely she'll have a bigger role to play in this limited series – you don't cast Toni Collette just to have her die right away. The series comes from Antonio Campos, director of Christine and The Devil All the Time, and American Crime Story writer Maggie Cohn.

Based on a true story, The Staircase follows the story of Michael Peterson, who will be played by Colin Firth. Peterson was a writer who was charged with murdering his wife Kathleen in 2001. In 2003, Peterson was convicted of the crime. However, eight years later, Peterson was granted a new trial after a judge ruled that a prosecution witness gave misleading testimony. Rather than go through a full trial again, Peterson took an Alford plea, which is where a defendant pleads guilty while also maintaining their innocence. After the plea, Peterson was sentenced to time already served and freed from prison. Deadline adds that the series "explores of life of Michael Peterson, his sprawling North Carolina family, and the suspicious death of his wife, Kathleen."

Peterson has always maintained that Kathleen actually fell down the stairs of their home while he was outside, and the docuseries The Staircase leans heavily into this theory. There's also an alternate theory that an owl caused Kathleen's death (yes, really – you can watch a featurette about that here). The docuseries originally ran on French TV in 2004. However, Netflix later bought the show and ordered three new episodes to wrap things up. While the docuseries is compelling, it's very much skewed towards Peterson's innocence, which puts its objectivity in question. Here's a trailer.

Campos and Cohn are writing the series and serving as showrunners and executive producers. "This has been a project I have been working on in one way or another since 2008," Campos said. "It's been a long and winding road, but well worth the wait to be able to find partners like HBO Max, Annapurna, co-showrunner Maggie Cohn and the incredible Colin Firth to dramatize such a complex true-life story."