When new mother Cora Tannetti takes a trip to the beach one day with her infant son and husband Mason, it looks like a regular family outing. What happens next—Cora killing someone with the knife she was using to peel fruit for her son, in front of dozens of witnesses—kicks off The Sinner, an eight-episode psychological thriller that explores why someone would commit such a gruesome act of violence for seemingly no reason.

For Jessica Biel, who plays Cora, depicting the challenges of motherhood and playing a darker role than what she's used to was deeply personal. The actress has a two-year-old son named Silas with husband Justin Timberlake, and she says it was only natural for her to draw from her own experiences for the character.

"It's personal for me," Biel told ELLE.com at the premiere of The Sinner on Monday in New York City. "I wouldn't be able to do this role if I didn't know what it was like to be a mom. If I wouldn't be able to see my son every day...I get emotional just thinking about it."

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"You think you're a selfless person, and then you realize you're not," Biel told Marie Claire in an August interview. "These little people come around, and they require so much, and your schedule is really not your own, nor is it important anymore, and it's very clear that it's your life now, revolving around this dude. I'm not that person who feels like, Oh, my whole life changes for my kid, but it does."

Biel also serves as one of the executive producers on the show, and was instrumental in bringing the 2008 book of the same name by Petra Hammesfahr to television. The Sinner is Biel's first major small-screen turn since her breakout role as Mary Camden on 7th Heaven.

While her fans will be interested in seeing her take on this darker role, it was also a change for Biel's husband Justin Timberlake. "With Justin, he's so happy for me," she told ELLE.com. "I always say he's my biggest fan."

Timberlake actually took to Instagram on Monday, posting a video preview to show support for his wife. "Ok, I know I'm not exactly fair and maybe biased here, but my wife's new show—@thesinnerusa—is amazing," he wrote in the caption. "It's like nothing I've seen her in before, and she's incredible in the role."

For Bill Pullman, who plays Detective Harry Ambrose, the hidden motive behind Cora's crime is what makes the show so interesting. His character becomes totally invested in the mysterious case, he says—especially because the answer isn't as simple as an investigator might hope.

"I got a good sense before I committed to the whole thing that there would be a journey to figuring that out," he told ELLE.com. "I think that kind of thing is a big challenge for writing. It's so interesting to stay in the murky zone of wondering what it is. But once it's revealed, there are lots of twists and turns to that. It's not a simple affair. There's no easy answer to say why somebody can do something as complicated as murder somebody else when they have no other inclinations to do so."

From: ELLE US