Who's Who Between Michael And Kathleen Peterson's Kids In HBO Max's 'The Staircase'

“The Staircase," the new HBO Max series, is a dramatization of French filmmaker Jean-Xavier de Lestrade’s docuseries of the same name, much of which focuses  on Michael Peterson’s family and their dynamics.

The filmmakers began filming Peterson and his family shortly after he was indicted for murder in connection with his wife Kathleen Peterson’s death. Her bloody and battered body was found at the bottom of a staircase in their North Carolina home in 2001. Peterson has always maintained that Kathleen, 48, must have fatally injured herself in a fall.

He was convicted of her murder in 2003 but released in 2017 from prison with time served after entering an Alford plea — a guilty plea whereby a defendant does not admit to the criminal act — to manslaughter charges to avoid a second trial.

The original docuseries began airing in 2004, though the filmmakers would revisit the case years later.

If you’re trying to figure out the blended family dynamics, we at Oxygen.com have got you covered.

First of all, there is Clayton and Todd Peterson, who Michael Peterson had with his first wife Patricia Peterson. Both were adamant that their father, played by Colin Firth in the new series, could not have killed their stepmom, played by Toni Collette.

Dane DeHaan and Patrick Schwarzenegger play the brothers in the series. 

Then, there are Margaret and Martha Ratliff, who were Elizabeth “Liz” Ratliff’s children. Liz, who was widowed in 1983, was friends with Michael and his first wife, Patricia. Liz died in 1985 at the age of 43 after a night out with Michael and Patricia. In fact, Michael had taken her home and was the last person to see her alive before her body was found the next day at the bottom of a staircase.

Her death was ruled an accident by German authorities, who determined that she had suffered a cerebral hemorrhage which led to her falling down a set of stairs and suffering serious injuries. Michael and Patricia acted as the girls' guardians after Liz's death, and they moved with Michael Peterson back to the United States, where Kathleen Peterson eventually helped raise them, too.

After Kathleen’s death, North Carolina authorities had Ratliff’s body exhumed and argued that she was murdered — a characterization with which Michael Peterson's lawyers took great issue. 

Sophie Turner plays Margaret and Odessa Young plays Martha in the series. Both maintained their father’s innocence.

The fifth child is Caitlin Atwater, Kathleen’s biological daughter with her former husband Fred Atwater; she was studying at Cornell when her mom died. Played by Olivia DeJonge, the new series shows how Caitlin was one of the first to believe that Michael could have killed her mother.