Jessica Biel as Cora Tannetti
In Season 1, episode 2 of “The Sinner,” Detective Harry Ambrose (Bill Pullman) remains doubtful that Cora Tannetti (Jessica Biel) killed Frankie Belmont (Eric Todd) randomly. USA Network

Detective Harry Ambrose is more determined than ever to find out why Cora Tannetti killed Frankie Belmont on Season 1, episode 2 of “The Sinner.”

According to the synopsis for the next episode of the USA series, Ambrose (Bill Pullman) continues his investigation into Frankie’s (Eric Todd) murder, despite Cora’s (Jessica Biel) repeated claims that it was a random killing.

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In the trailer for the episode, Ambrose is convinced that Cora is hiding something from him, so he pays her a visit at the county jail and asks her more questions, but Cora is sticking with her initial statement.

“I didn’t know him. Something in me just snapped,” Cora tells the detective, after once again being asked why she murdered Frankie.

Apparently, Ambrose doesn’t still buy Cora’s explanation so he tells her that he’s going to keep digging until he finds the truth.

“I’m trying to help you,” the detective assures Cora. “You could get your life back.”

“What makes you think I want my life back?” the detainee bluntly replies.

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Ambrose’s theory that there’s more to the murder than what meets the eye was somehow confirmed when he got to talk to Patrick, a bystander who witnessed the crime, at the end of the series premiere.

During their meeting, Ambrose asked Patrick why he didn’t try to stop Cora from attacking his friend, Frankie, when he was just sitting near the victim. Patrick revealed that he wasn’t able to save Frankie because he was shocked after he saw his friend grab Cora’s arm, right after she stabbed him for the first time. “And the thing is, Frankie’s a strong guy,” Patrick told Ambrose.

When the detective asked why Frankie didn’t force Cora off when she attacked him, Patrick said: “It looked like he recognized her. When he saw who [was stabbing him], he let her go.”

Elsewhere in next week’s episode, Cora’s husband, Mason Tannetti (Christopher Abbott), struggles to come to terms with the secrets from his wife’s past. While it looks like Cora’s backstory will continue to unravel as the series continues, it was revealed in the show’s first episode that Cora had a strained relationship with her mom. In a flashback scene in the series premiere, Cora’s mother disturbingly blamed her for her little sister being born unhealthy.

Why do you think Cora killed Frankie? Sound off in the comments section below!

“The Sinner” Season 1, episode 2 airs on Wednesday, Aug. 9 at 10 p.m. EDT on USA Network.