Gwen was actually talking to the BH killer all along.

• When I play back Rob’s actions they made no sense whatsoever and were in no way justified. Rob was convinced that Gwen knew John was the BH Killer and therefore his intention was to make her confess and then kill her. BUT WHY?! There was nothing to gain by going through all that trouble to hire Gwen and get close to her. I wish he was unsure about whether Gwen knew or not and for it to become a cat and mouse game with Rob trying to find out the truth. Or even make him psychologically crazy and that he just wanted to toy with her, anything!
• Why on earth did Rob treat Gwen so well given his intentions to kill her? For example he gave her a ring that meant a lot to him. Did anyone else raise an eyebrow when Rob gave Gwen the ring, slept with her and then questioned her about John?
• During the reveal Rob had come to kill Gwen but he was interrupted by the detective. I was scratching my head wondering why she did not say anything and turn him in.
• Gwen’s thoughts on whether Randall was guilty or not got a bit drawn out. It was too clear to the reader that it wasn’t him, so it made Gwen’s bias seem more silly to me rather than interesting. I was thinking, omg just realise it already!
• The incident with Luke and the stolen keys didn’t add much to the story because we find out from Rob anyways that Randall’s MO was young girls. And the lost keys only led to Gwen running to Rob. I understand the need to throw red herrings and distractions but this didn’t really add anything to the story.
• What happened to Rob’s dead wife?! I thought there would be a huge revelation or link but it seems the main purpose was to give Rob a sad backstory and to help justify his crazy actions such as doing his own investigation and withholding information about the BH Killer and his intentions with Gwen (Read Jen’s spoiler points she summed it up nicely!)
• I’ve never studied law but the conflict of interests between Rob and Randall seemed too farfetched for Rob to be his attorney. Though I was willing to overlook this.