The evidence is confusing and inconclusive. The prosecution (including Parker Posey as a heavily made-up district attorney) claims he beat his wife to death after she found gay pornography on his computer. Helped by his lawyer (Michael Stuhlbarg), Michael (Firth) claims Kathleen (Collette) drank too much and fell down those stairs.

“Staircase” lays out the case for and against Michael. ‘The Staircase’ documentary: What you need to know about the real Michael Peterson And that family is meticulously acted by a stellar cast, particularly its younger members. It is less about how Kathleen Peterson died and more about what lies and half-truths can do to a family. “Staircase” is a pretty standard highbrow crime drama, one with unreliable narrators, angry lawyers and emotional breakdowns.

Colin Firth as Michael Peterson and Toni Collette as Kathleen Peterson in “The Staircase” on HBO Max.