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A guide to the star-studded cast of 'The Staircase' and the real people they play

Starring Colin Firth and Toni Collette, "The Staircase" is HBO Max's true crime series about the 2001 death of Kathleen Peterson and its aftermath.

The true crime documentary series “The Staircase“ first aired in 2004, and has continued to evolve since then.

Directed by Jean-Xavier de Lestrade, “The Staircase” followed the trial of novelist Michael Peterson, who was charged with murdering his wife, Kathleen Peterson, in 2001. Kathleen was found dead at the bottom of the staircase of their Durham, North Carolina home. Michael, to this day, maintains his innocence.

The sequel, “The Staircase II: The Last Chance” (2013) was filmed about 10 years after Michael was found guilty of first-degree murder in 2003. Three final episodes of "The Staircase" were released in 2018, ending with Michael leaving prison a free man after entering an Alford plea to involuntary manslaughter, which allows him to maintain innocence while acknowledging the prosecution has enough evidence to convict. The entire 13-episode saga is now streaming on Netflix.

Now, “The Staircase” is being adapted into a drama on HBO starring Colin Firth and Toni Collette as Michael and Kathleen Peterson. The rest of the cast is star-studded, filling out the many people connected to the case, including Michael Stuhlbarg as defense lawyer David Rudolf and Olivia DeJonge as Kathleen Peterson's daughter, Caitlin Atwater.

Out May 5, “The Staircase” is part of a wave of ripped-from-the-headlines dramas out this spring including “The Dropout” about Elizabeth Holmes and “The Girl From Plainville” about Michelle Carter and the suicide-by-texting case.

The fictionalization adds a level of intimacy to the story, as characters grapple with hearing revelations first-hand, not through an interview with a documentarian. What it doesn’t necessarily add is answers: In interviews, the cast spoke about grappling with the lingering mysteries of the case, though it is now considered closed.

“I very much wanted to err toward finding my own interpretation,” First told Vanity Fair of his character, Michael. “That’s partly because I don’t really feel I have answers.”

Here’s your guide to the many characters filling up this particularly winding journey.

Michael Peterson (played by Colin Firth)

Pictured, l-r: Michael Peterson and Colin Firth.
Pictured, l-r: Michael Peterson and Colin Firth.AP, HBO Max

Michael Peterson, now 78, is a war novelist and former newspaper columnist. He unsuccessfully ran for mayor of Durham in 1999, his campaign felled by false claims of injuries sustained in combat during the Vietnam War, per WRAL, which he later admitted to the Durham News & Observer. At the time of Kathleen’s death, Michael was running for city council, per the Durham News & Observer.

Michael is also the figure at the center of “The Staircase.” As revealed in the trial, per CNN, at 2:40 A.M. on Dec. 9, 2001, Michael called 911 to say his wife, Kathleen, had fallen down the stairs and was unconscious. In “The Staircase” documentary, Michael claimed that he had been sitting by the pool, only to stumble upon the accident when he walked into the house.

Michael was charged with Kathleen’s murder, and was found guilty in 2003. He was granted a retrial in 2011, but never went to court again. In 2017, Michael left prison after entering an Alford plea, which allowed him to plead guilty to involuntary manslaughter without admitting guilt. He continues to maintain his innocence.

As the trial unfolded, parts of Michael’s past emerged. The prosecution brought up Michael’s bisexuality and extramarital affairs with men at the trial. In “The Staircase,” Michael said that Kathleen knew about and was “comfortable” with his bisexuality. 

Michael had also been connected to a woman in Germany who met a similar fate to Kathleen. Michael and his first wife, Patricia, were living in West Germany and befriended a neighbor, Elizabeth Ratliff. On November 24, 1985, Ratliff was discovered at the bottom of the stairs, per NBC. Authorities, at the time, said she died of spontaneous intracranial hemorrhage, a stroke, and natural causes, per NBC.

Michael got custody of Ratliff’s two daughters. He denies any involvement with Elizabeth’s death. Documentarian de Lestrade believes Ratliff’s death was an accident: “There is no doubt,” he told Metro

"The Staircase" marks Firth's first TV project in 25 years, per Vanity Fair. He is known for films like "Bridget Jones's Diary" and "The King's Speech,"

Firth said he tried to keep an open mind while playing Michael, maintains his innocence. “It wouldn’t have been possible and it certainly would have defeated the purpose of the exercise if I did take up a single position and impose my judgment because then I wouldn’t have been free to explore an alternative interpretation. And (the show) does play with different interpretations,” Firth said during the Television Critics Association’s winter press tour.

Pictured, l-r: Kathleen Peterson and Toni Colette.
Pictured, l-r: Kathleen Peterson and Toni Colette.NBC, HBO Max

Kathleen Peterson (played by Toni Collette)Toni Collette, who was recently in the Netflix series “Pieces of Her,” plays Kathleen Peterson, an executive for the telecommunications firm Nortel who married Michael Peterson in 1997.

They had a blended family: Kathleen was mom to Caitlin Atwater, and Michael had four kids (two biological sons and two adopted daughters).

In 2001, when she was 48, Kathleen was found unconscious, in a pool of her own blood, at the bottom of the stairs in her Durham, NC home. She died from her injuries.

Michael’s defense team argued that Kathleen had slipped on the stairs after imbibing Valium and wine, per NBC.

The prosecution painted a different picture. The lacerations on Kathleen’s scalp, the prosecution argued, were from Michael bludgeoning her to death with a blow poke, a fireplace tool. “It just never occurred to Michael Peterson that people wouldn’t believe him when he said she fell down the stairs,” Greg Mead, the assistant district attorney, said in “The Staircase” documentary.

While Kathleen’s death is the inciting incident for the series, she’s in much of the show. Collette acts out different possible ways that Kathleen died — including the owl theory, which theorizes that Kathleen was attacked by a barred owl. The owl theory was first introduced by the Petersons’ neighbor, attorney Larry Pollard.

David Rudolf (played by Michael Stuhlbarg)

Pictured, l-r: David Rudolf and Michael Stuhlbarg.
Pictured, l-r: David Rudolf and Michael Stuhlbarg.AP, HBO Max

“The Staircase” follows the efforts of Michael’s defense team, headed by attorney David Rudolf. Rudolf remained Michael’s lawyer for 15 years.

Rudolf called the first trial a “character assassination” in an interview with Digital Spy, as the prosecution, he claimed, could not come up with neither a motive nor a murder weapon: “There was no evidence of motive that ever stood up to cross examination,” he said.

Stuhlbarg was in “Dopesick” and “The Looming Tower,” as well as “Call Me By Your Name.”

Freda Black (Parker Posey)

Pictured, l-r: Freda Black and Parker Posey.
Pictured, l-r: Freda Black and Parker Posey.AP, HBO Max

Freda Black was the assistant district attorney and prosecutor in the Peterson case. Black died in 2018.

After many mockumentaries, including “Best in Show” and “Waiting for Guffman,” Posey is in a show based on a real documentary.

Caitlin Atwater (played by Olivia DeJonge)

Pictured, l-r: Caitlin Atwater and Olivia DeJonge.
Pictured, l-r: Caitlin Atwater and Olivia DeJonge. AP, HBO Max

Caitlin Atwater is Kathleen’s daughter from her first marriage to Fred Atwater. When her mother died, Caitlin was a freshman at Cornell University, per WRAL.

At first, Atwater supported her stepdad. “My mother and Mike had an absolutely loving relationship. There’s no way that either of them would ever wish any sort of harm on the other one,” Caitlin said, serving as the main spokesperson for the family, as seen in “The Staircase” documentary.

Atwater later switched sides, and ended up being a witness for the prosecution. She reached a $25 million wrongful death settlement against Michael in 2007, per AP, but says she has not been paid as of 2017. According to WRAL, Atwater said her "intent" behind the lawsuit was so Michael could not "profit from the crime."

DeJonge, an Australian actor, was also in the Netflix series “The Society” and will play Priscilla Presley in the upcoming Elvis biopic.

Candace Zamperini (played by Rosemarie DeWitt)

Pictured, l-r: Candace Zamperini and Rosemarie DeWitt.
Pictured, l-r: Candace Zamperini and Rosemarie DeWitt. AP, HBO Max

Kathleen’s sisters, Candace Zamperini and Lori Campbell, continue to believe Michael is guilty. Zamperini gave an impassioned speech for her sister and the "evils of (her) death" depicted in episode 13 of “The Staircase.”

In her courtroom testimony in 2003, Zamperini told jurors she gifted the Petersons the blow poke that the prosecution raised as a potential murder weapon.

Zamperini is played by Rosemarie DeWitt, of “Mad Men” and “La La Land.”

Todd Peterson (played by Patrick Schwarzenegger)

Pictured, l-r: Todd Peterson and Patrick Schwarzenegger
Pictured, l-r: Todd Peterson and Patrick SchwarzeneggerAP, HBO Max

Todd Peterson is the second of Michael’s two sons from his marriage to Patricia Peterson. He supports his father in the documentary series.

Todd is played by Patrick Schwarzenegger, who told TODAY this was a “dream role.” He said that he watched “The Staircase” during COVID and became “obsessed” with the story.

Clayton Peterson (played by Dane DeHaan)

Pictured, l-r: Clayton Peterson and Dane DeHaan
Pictured, l-r: Clayton Peterson and Dane DeHaanNBC, HBO Max

Clayton Peterson is Michael’s oldest son from his first marriage to Patricia Peterson. Clayton continues to stand by his father.

“The Staircase” documentary doesn’t mention that Clayton, at 19, was sentenced to four years in a federal penitentiary for planting a pipe bomb outside of a Duke University administration building. The bomb did not explode.

Dane DeHaan was in the 2021 miniseries “Lisey’s Story” and starred in the sci-fi movie “Valerian and the City of a Thousand Planets.”

Margaret Ratliff (played by Sophie Turner)

Pictured, l-r: Margaret Ratliff and Sophie Turner.
Pictured, l-r: Margaret Ratliff and Sophie Turner. AP, HBO Max

Michael Peterson was the legal guardian of Margaret and her sister, Martha. The Ratliff sisters stood by Michael through the trial, as evidenced by "The Staircase" documentary.

The Ratliff sisters’ biological father, George Ratliff, was in the U.S. Air Force and died while on assignment in 1983. Their mother, Elizabeth, was found dead at the bottom of her stairway in Germany in 1985. Michael became the orphaned girls’ guardian. Elizabeth’s body was exhumed during Michael's trial. An autopsy ruled her death a homicide, WRAL reported. Michael denies involvement in her death.

Sophie Turner is best known for her work in “Game of Thrones.”

Martha Ratliff (played by Odessa Young)

Pictured, l-r: Martha Ratliff and Odessa Young
Pictured, l-r: Martha Ratliff and Odessa YoungAP, HBO Max

Martha Ratliff is Margaret's younger sister. Both sisters were in college when the trial unfolded: Martha at the University of San Francisco, and Margaret at Tulane University.

Pictured, l-r: Martha Ratliff and Margaret Ratliff; Odessa Young and Sophie Turner.
Pictured, l-r: Martha Ratliff and Margaret Ratliff; Odessa Young and Sophie Turner.AP, HBO Max