People Magazine Investigates looks at the presumed murder of the woman who vanished in October 2018

Cheryl Coker was never without her phone.

Bubbly and quick to laugh, the mother and grandmother was always checking in with family and friends, who described her as an open book — so much so that her closest pals knew all about the recurring struggles in her marriage.

Get push notifications with news, features and more.

When Cheryl told them she and her husband Bill, whom she married in 1998, had become “swingers,” engaging in sex with others outside of their marriage, her friends didn’t judge her.

But in the summer of 2018, Cheryl told them Bill had a girlfriend he was refusing to drop.

He didn’t want a divorce, Cheryl told them; he wanted to keep up appearances until their youngest daughter finished high school, she told them.

Cheryl filed for divorce anyway on September 21, 2018 — and 11 days later on Oct. 2, the day after police say Bill returned from a trip to Florida accompanied by their youngest daughter and the woman he’d been seeing, Cheryl appeared to vanish. The case is the subject of tonight’s episode of of People Magazine Investigates, airing at 10 p.m. ET on Investigation Discovery. (An exclusive clip is above.)

Image zoom Cheryl Coker Courtesy Coker Family

A find-my-phone app tracked Cheryl’s cell to her locked car, which was found later that same day in a strip mall parking lot less than a mile from the home she and Bill still shared.

Want to keep up with the latest crime coverage? Sign up for PEOPLE’s free True Crime newsletter for breaking crime news, ongoing trial coverage and details of intriguing unsolved cases.

“There was a lot of personal items inside her SUV,” police detective Travis Abney tells PEOPLE. “We found her purse and her credit cards. That’s not normal. No one is going to leave their ID, their money, their credit cards, their cell phone especially.”

Image zoom Bill and Cheryl Coker Facebook

Police have since labeled the case a homicide, and identified Bill as a suspect. But with insufficient evidence to warrant an arrest, he has not been charged. He did not respond to PEOPLE’s request for comment.

Thinking back on Cheryl’s missing items, including the 46-year-old’s phone, Abney says, “It started becoming more and more bizarre to me at that point.”