"It did look so similar," she told E! News' Francesa Amiker. "And then, [Justin] was like, 'Well, wait a minute, you kinda look like my mom from the '80s.' And I said, 'I kind of look like my grandmother from the '80s.' The perms were big. I had a perm."
In addition to getting into character physically, Biel also focused on the themes present during that time, especially in how they factored in Montgomery's relationship with her friend turned victim Betty Gore (Melanie Lynskey), such as "guilt and shame and rage and repressions and inability to communicate."
"I'm just endlessly fascinated by these human moments where human beings get pushed to the edge," Biel said about telling the story of the gruesome 1980 murder. "And I really believe that we're all capable of anything and everything."
She continued, "That phrase 'never say never' is really very true and I'm just always wondering, like, 'Am I capable of something as horrible as that?' And I like to put my feet in those shoes and sort of walk around a little bit."
Having not been on a red carpet in three years, Biel and Timberlake turned the occasion into a makeshift date night, though their kids -- Silas, 7, and Phineas, 2 -- made their plans a little difficult.
"I mean, try to get a good night's sleep, which we didn't because our kids were up, of course," Biel said about getting ready for the premiere. "As you know, every parent knows, like, they know when you're trying to go out. They do, those kids."
Despite the sleep deprivation, the actress did get to enjoy a relaxing Mother's Day weekend with her family of four.
"I got the most beautiful flowers, and [Justin] wrote me these beautiful cards," said Biel. "And then, my kids made these incredible T-shirts, like, decorated a T-shirt and wrote, 'Best Mom In Life,' and a canvas bag with handprints and footprints. It was just so sweet and perfect."
Check out the full interview in the clip above.
The five-part series "Candy" premieres with new episodes daily through Friday, May 13 on Hulu.