'The Staircase' cast 'freaked out' when they first heard Colin Firth's voice for his character, according to Parker Posey

• Parker Posey says "The Staircase" cast "freaked out" when they heard Colin Firth in character.
• "I just got creeped out because he was so uncanny," Posey said in a new interview.

Colin Firth stars as novelist Michael Peterson in HBO Max's new drama "The Staircase," and Firth's costar Parker Posey said the actor absolutely nailed his performance.

After being asked about Firth's "spot-on" voice for Peterson, Posey revealed to the New Yorker that the entire cast had a strong reaction to hearing him read his lines in character for the first time.

"We all freaked out at the Zoom readings," Posey, who plays assistant district attorney Freda Black, said of Firth's voice. "I just got creeped out because he was so uncanny. He just really stepped it up."

Peterson was accused of killing his second wife Kathleen after she was found dead at the bottom of a staircase in their North Carolina mansion in 2001.

The HBO Max drama is inspired in part by the true-crime documentary series of the same name, and follows Peterson (Firth) and his blended family as they try to come to terms with Kathleen's death, and Peterson's possible guilt.

Posey also told the New Yorker that the entire cast — which also includes Sophie Turner, Toni Collette, Patrick Schwarzenegger, and Michael Stuhlbarg — frequently discussed whether or not the real-life Peterson was responsible for Kathleen's death.

"Every weekend, we got together and talked about it," the "Dazed & Confused" actress said. "You go up and down the staircase, and think, Is he guilty? Is he innocent? Did he do it? Did he?"

"I don't want to think that he did something like that. He's such an interesting person. He's such a character," Posey added.

As the drama shows, Kathleen's December 2001 death immediately raised suspicions. Authorities were called to the Peterson home after a frantic 911 call by Michael — upon arriving, they found Kathleen unresponsive at the bottom of a staircase in the home, covered in blood. Michael told police that she'd fallen down the steps.

Investigators soon identified the former novelist as a person of interest, and Michael later turned himself in after being indicted for Kathleen's murder. Following a lengthy and highly-publicized trial, Michael was convicted of first-degree murder and sentenced to life in prison in 2003.

However, after it was revealed that one of the prosecution's key witnesses had lied while under oath, a judge vacated the original jury's verdict in 2011. After submitting an Alford plea in 2017, Michael was released for time served.