The HBO Max miniseries The Staircase is based on a true story, and The Staircase cast includes an all-star group of actors who look uncannily similar when compared to their characters' real-life counterparts. The four-part series is a dramatic retelling of the 2001 death of Kathleen Peterson and the emotional legal aftermath that followed. In one of the longest trials in the history of North Carolina, Kathleen's husband, Michael Peterson, was sentenced to life without the possibility of parole for her murder.

The Staircase, like the original 2004 true-crime documentary series of the same name, raises questions regarding what really happened. Michael and Kathleen Peterson seemed to live a normal life in Durham, North Carolina, but when she was found dead at the bottom of their staircase on the evening of December 9, 2001, the tragedy turned their family upside down. The evidence surrounding the case is still heavily debated. As is portrayed in the HBO Max miniseries, the story was first chronicled in a French documentary, also called The Staircase, and was also explored by a number of popular American true-crime television series, including Forensic Files, Dateline NBC, and Cold Case.

Colin Firth As Michael Peterson

Michael Peterson appeared to be a happy and successful man. He served an honorable military career and became a published author, newspaper columnist, and mayoral candidate. Michael loved his wife and children, and for all intents and purposes lived an average life. The death of his wife Kathleen, however, sent his life into turmoil. In 2003, Michael was put on trial and then sentenced to life in prison without the possibility of parole. He was eventually released on bail and wore an ankle monitor in 2011 after the validity of the trial was brought into question.

Despite maintaining his innocence throughout the entire case, Michael took an Alford deal in 2017, declaring guilt without sufficient evidence in order to go free without serving additional time. In addition to The Staircase cast, Colin Firth is a well-established actor in the world of film and television. Known for his roles in such movies as A Single Man, The King's Speech, and recent roles in Operation Mincemeat and Rye Lane. Firth has won several accolades throughout his career, including an Academy Award, two BAFTAs, and a Golden Globe, and he was appointed Commander of the Order of the British Empire in 2011 for his service in the dramatic arts.

Toni Collette As Kathleen Peterson

Kathleen Peterson was a loving mother and had a successful career. After becoming the first woman to be accepted into the Duke University engineering program, she became a telecommunications executive. Kathleen was only 48 years old when she died of blood loss at the bottom of the stairs in the Petersons' mansion in North Carolina.

Toni Collette played Kathleen in The Staircase cast. She is another established veteran in the world of acting. Making her debut in the 1990s, Collette gained mainstream recognition for her role as Lynn Sear in The Sixth Sense. Since then, she appeared in movies across a wide variety of genres, such as Rian Johnson's Knives Out, as well as Little Miss Sunshine and Hereditary. In 2023, she joined the cast of the sci-fi series The Power on Prime Video while taking the lead role in the mafia comedy movie Mafia Mamma. Collette has also earned a variety of awards throughout her career, including a Primetime Emmy and a Golden Globe.

Sophie Turner As Margaret Ratliff

Although Margaret Ratliff was not the biological child of either Michael or Kathleen Peterson, she loved her adoptive mother and remained loyal to her adoptive father throughout the trial. The biological parents of Margaret and her sister, Martha, died when the girls were young, and they were taken in by Michael and his then-wife, Patricia Peterson, while the couple was living in Germany.

In addition to The Staircase cast, Sophie Turner made her acting debut in 2011 playing Sansa Stark in Game of Thrones. Since then, Turner has played Jean Grey in the X-Men franchise and appeared in such movies as Barely Lethal and The Thirteenth Tale. She also lent her voice to the HBO Max Original animated series The Prince. She also signed on for the lead role in the British TV series Joan.

Patrick Schwarzenegger As Todd Peterson

Todd Peterson is the youngest son of Michael Peterson and his ex-wife, Patricia Sue. He was by his father's side from the very beginning of the case, helping him navigate both the immediate aftermath of Kathleen's death and the trial process. At the time of the incident, Todd ran a website called Futazi, which provided advice on various topics to teenagers.

As the son of Arnold Schwarzenegger, Patrick Schwarzenegger is no stranger to Hollywood. His first movie appearance was at age 10, in The Benchwarmers. Schwarzenegger went on to star in such movies as Midnight Sun, Daniel Isn't Real, and Moxie. Schwarzenegger was cast to appear as Golden Boy in The Boys' spinoff series Gen V and appeared in the 2022 Prime Video series, The Terminal List.

Odessa Young As Martha Ratliff

Like her sister Margaret, Martha was not the biological daughter of the Petersons, but she too remains loyal to her adoptive father to this day. Martha had left for college in San Francisco shortly before their lives were turned upside down by Kathleen's death and the resulting fallout. Both Margaret and Martha appeared frequently in interviews and documentaries in support of their father.

After making her start in Australian television, Odessa Young broke out into the world of film with The Daughter alongside Geoffrey Rush and Sam Neill. Since then, her filmography has expanded to include roles in such movies as A Million Little Pieces, Shirley, and The Professor. Young is also known for playing Frannie Goldsmith in the recent television adaptation of Stephen King's The Stand. In 2023, she appeared in the Jese Eisenberg movie Manodrome.

Dane DeHaan As Clayton Peterson

Clayton Peterson is Michael Peterson's eldest son. After spending some time in prison for attempting to firebomb the Duke University administration building, Clayton got out of trouble and is now married with two children. Like most of his siblings, Clayton remained loyal to his father during the murder trial and prison sentence, just as his father had been loyal to him.

In addition to The Staircase cast, Dane DeHaan has appeared in a variety of films and television series throughout his career. From the psychological horror A Cure for Wellness to the space opera Valerian and the City of a Thousand Planets to playing the villainous Harry Osborn in The Amazing Spider-Man 2, DeHaan has acted in a wide spectrum of roles. In 2023, he has a role in one of the biggest movies of the year - Christopher Nolan's Oppenheimer.

Olivia DeJonge As Caitlin Atwater

Caitlin Atwater is the biological daughter of Kathleen Peterson and her ex-husband, Fred Atwater. Unlike her stepsiblings, Caitlin did not stand by Michael's side. Although she supported him in the beginning, autopsy photos of her mother's body turned her into a key witness for the prosecution. Caitlin would go on to file a wrongful death claim against Michael Peterson, and she was awarded $25 million in 2008.

Olivia DeJonge played Caitlin in The Staircase cast. She began a career in the world of film and television starting with her 2014 feature film debut, The Sisterhood of Night. Since then, DeJonge has appeared in such movies as The Visit and Better Watch Out, as well as the television series The Society. DeJonge also starred in Baz Luhrmann's Elvis biopic, portraying Priscilla Presley.

Michael Stuhlbarg As David Rudolf

David Rudolf served as Michael Peterson's defense attorney during his trial. Rudolf specializes in covering high-profile cases. He helped to overturn the wrongful conviction of Alan Gell, return hard-earned money to Vietnamese immigrants Hai and Oanh Le Nguyen after it was seized by the federal government, and got several accused murderers acquitted. Rudolf firmly believed in Michael's innocence, continuing to represent him long after his client could afford his services.

In addition to The Staircase cast, Michael Stuhlbarg is a well-known character actor with a very successful career. After his breakthrough role in A Serious Man in 2009, Stuhlbarg became well known for his performances in such movies as Call Me By Your Name and Best Picture winner The Shape of Water. Stuhlbarg has also played roles in various television series, including Sy Feltz in Fargo and Richard Sackler in Dopesick.

Rosemarie DeWitt as Candace Hunt Zamperini

Like Caitlin Atwater, Candace Hunt Zamperini firmly believed that Michael had caused the death of Kathleen — her sister. Candace became an integral force in the case against Michael, even raising the possibility herself that the fire poker she had gifted her sister had been used as a murder weapon. Candace has remained outspoken about her beliefs, appearing in frequent interviews and documentaries to tell her side of the story.

Rosemarie DeWitt played Candace in The Staircase cast. She has appeared in many films and television series throughout her career, ranging from horror to comedy. DeWitt is best known for her roles in television series like Standoff, in which she co-starred alongside her future husband, Ron Livingston, and The United States of Tara. DeWitt also starred in the 2015 Poltergeist remake. DeWitt joined The Boys cast in 2023 as Hughie's mom and has a lead role in the Disney+ movie Out of My Mind.

Parker Posey As Freda Black

Freda Black was the former Durham County prosecutor who served as the main prosecutor against Michael Peterson. Black played an instrumental role in securing the murder conviction, playing on Peterson's bisexuality to create a strong motive that won over the jury. Black passed away in 2018 as a result of end-stage liver cancer caused by chronic alcoholism.

In addition to The Staircase cast, Parker Posey is a veteran actress with a very impressive filmography. Having appeared in a wide variety of films and television series, she is best known for her roles in Scream 3, Dazed and Confused, and Blade: Trinity. Posey has also lent her voice to animated series, with cameos for The Simpsons, Futurama, and Skylanders Academy. In 2023, she appeared in the A24 movie, Beau is Afraid and has a role in the Prime VIdeo series based on the movie, Mr. & Mrs Smith.