Plus, why Toni Colette’s role in the HBO Max drama is so crucial.

In other words, viewers know Michael Peterson.

So how do you cast him?

Harrison Ford and Colin Firth

Harrison Ford and Colin Firth.Alberto E. Rodriguez/Getty Images; Samir Hussein/WireImage

And at first, they thought they’d found their answer in none other thanHarrison Ford.

“We originally had been to Harrison Ford,” Campos says.

“But we parted ways because he had to go doanIndiana Jones.”

Colin Firth and Toni Collette in ‘The Staircase’

Colin Firth and Toni Collette in ‘The Staircase’.HBO Max

Just like that, they were back to square one.

That’s whenColin Firth’s name came up.

And it’s so vicious and it’s so ferocious.

It was this reminder of the danger that he could also play."

Then there’s the question of Kathleen Peterson, the murder victim.

It’s a pivotal role for the show, but a particularly tricky one.

And so we needed an actor that made her feel alive up until that point.

And I mean,Toni Coletteis one of the most alive people on and off screen."

The first three episodes ofThe Staircaseare streaming now on HBO Max.