S4 episode 6 Aired on August 7, 2016

Warning: Contains Spoilers

Motive Case Report: #406

The Killer: Cindy Vernon, a dedicated music teacher

The Victim: Tracy Blaine, a blogger and stepmother

The Discovery: Tracy is found impaled on a tree limb in Central Park. (It’s as gross as it sounds.)

The Investigation: Brian interviews Jill Dawes, the last person Tracy spoke to. She used to nanny for Steven’s son, Owen. She was leaving because Tracy was having trouble bonding with Owen.

When Jill learns that Tracy was found in Central Park, she says Tracy would only go there with Owen so he could play with his remote-control boat. Detectives find the boat and the investigation turns into a search operation.

Owen’s dad Steven is out of town for work. Steven owns an organic juice company that had an E. Coli outbreak which sickened 27 people and killed three, including a child, eight months ago.

Detectives pick up Steven from the airport. After the appropriate level of panic, he tells Angie that Owen suffers from seizures, vomiting, and tremors, but doctors don’t know why. They show Steven a sketch from a witness of Cindy but Steven doesn’t recognize her.

Meanwhile, Cindy has Owen safe and relatively happy in a motel, except he wants to see Tracy and he’s throwing up.

Tracy posted a video on her blog just before she was killed. She posted a lot of personal information, including all the trials of Owen’s illness. One of her readers says Tracy emailed her, worrying Steven was cheating on her. Angie decides to bite the bullet and pony up for the Affair Jar, calling it early.

Angie shares the emails with Steven, who is shocked his wife was unhappy. She sounds like a martyr in her emails, like she’s very put upon taking care of Owen. Steven says he didn’t want to travel all the time, but was trying to save his company so he’d have the money to pay for his son’s care.

Angie sees Det. Paula Mazur looking queasy in the break room and Mazur confesses that she’s pregnant, the father is the man she just broke up with because he wanted to get serious and she didn’t. Oops.

Angie and Paula visit Cindy’s house and talk to her boyfriend, Dean, who tells them Cindy said she needed a few days to herself.

On Cindy’s tablet, they find detailed logs of Tracy and Owen’s movements. They also see a note referring to Aiden Harris, a boy in Cindy’s class about Owen’s age who died four years ago.

Paula talks to his father, who says Aiden had a mysterious illness and died. Tracy was his ex-fiancée, they broke up after Aiden died.

Cindy tries to leave the motel with Owen, but the desk clerk sees him in her car and calls the police. Another search of visitors to the blog turns up Cindy.

Cindy pulls up to a bus stop with Owen and realizes he’s having a seizure in the back seat. She races him to a hospital and leaves him with EMS.

Later in the hospital, Angie talks to Owen, who remembers that Tracy gave her candy at the park then went to go talk to her friends, then he left with Cindy because she told him she was taking him to Tracy.

Back at the station, forensics finds that Owen has sodium poisoning: his candy was fruit flavored antacid that could easily kill a small child in big quantities. Aiden Harris had the same symptoms. Tracy poisoned them both, likely suffering from Munchausen’s by proxy (drawing attention to herself through other’s illness). Realizing how close Cindy was to Aiden, the detectives head to Aiden’s grave and find Cindy there. She goes with them calmly.

At the hospital, the doctors say Owen will make a full recovery.

Background: Last year, Cindy was pregnant but her baby was stillborn. One day, Cindy was at the park with her boyfriend and saw Owen there with Tracy. She began following him to protect him from Tracy.

The Motive: Cindy was watching Owen at the park when Tracy saw her. Cindy tried to run away but when Tracy confronted her, Cindy threatened to call the police and report Tracy for hurting the boys. When Tracy shoved her, Cindy shoved back, accidentally impaling her on a tree branch. But then when Tracy pleaded for help, Cindy took the opportunity to save Owen and skewered Tracy further.

The Trial: Det. Brian Lucas asks a prosecutor about Tim Kelly, the man who attacked Dr. Betty Rogers. The prosecutor has concerns about the case because Rogers never saw his face and she lifted the fingerprints off herself.

Later, Brian meets with a man who claims he saw Tim Kelly outside the station the day of the attack. He’s coming forward now because he wasn’t sober at the time -- at least that’s the story Brian is coaching him to offer. In exchange, Brian will make his drug possession charges disappear. That will definitely turn out well.