Colleen Dexler is the stalker of Dr. Greg Ross and the prime suspect in the murder of his wife, Lisa Vanston Ross.
Background[]
Colleen Dexler previously dated Greg, a dentist, before her overbearing and disapproving mother Joanna arranged Colleen's sister Morgan to be Greg's girlfriend and eventual wife, always doting on Morgan more and degrading Colleen into the place she wanted her to be. Unfortunately, because the marriage was unhappy, Morgan had an affair, and when Greg found out, he killed her with dioxin poisoning out of resentment. Colleen realized the truth and decided Morgan deserved it, still wanting Greg to herself from an obsession of never having him for the rest of her life.
When she found out Greg married another woman, Lisa Vanston Ross, Colleen finally snapped and plotted to murder her for ruining Colleen's chances of getting to Greg. She stalked Lisa through her life and got acquainted with her at pub trivia bowls, using the established confidence to gain her trust. To evoke Greg murdering Morgan to get his attention, she anonymously set up an "affair" where she seduced Lisa in online chatting, exploiting her cocaine addiction as a means of killing her. Sending her a package laced with dioxin, she instructed Lisa to administer the drug into her vagina so it would be absorbed directly into her systems, then waited for the dioxin to take affect.
Beast[]
It did when the next day, Lisa collapsed in a parking garage red and vomiting. She was rushed to the hospital where she swiftly developed chloracne, a side effect of dioxin which also showed in Morgan when she was murdered. After Lisa's personal statement to Major Case, she eventually dies from the toxin's effects. Colleen then arranges an appointment at Greg's office to harass him, confessing to Lisa's murder directly to him and swearing to keep his crime a secret if he does so with hers. When the connections between the two murders are made, Greg is arrested on suspicion, but the detectives accurately expected Greg to take the bait and pin the murders on Colleen.
This gives enough conflicting testimony and suspicion on her to bring her in. Starting with the ploy of knowing she never got over Greg, they then say Greg pinned both murders on her, Joanna present as a shocked witness. Colleen panics and says she only killed Lisa, then starts professing her love for Greg to explain her motives. As the detectives arrest her and take her out, Joanna berates her for being the daughter she hated, with Colleen shooting back if she was married to Greg, he'd have never killed her as she would've always been a faithful, loving wife. Colleen confessed to Lisa's murder and was imprisoned.