On Aug. 13, 2018, the Colorado dad killed his 15-weeks-pregnant wife and their two young daughters

Lifetime Announces Movie About Chris Watts 1 Year After He Murdered His Wife and 2 Daughters

Lifetime is making a movie about the tragic murders of Shanann Watts and her two young daughters a year ago by her own husband, Chris Watts, PEOPLE can exclusively announce.

Based on real-life events and taped confessions, The Chris Watts Story, a working title, will chronicle the months that led up to the horrific crime, piecing together the Colorado dad’s possible motives.

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Sean Kleier (Odd Mom Out) has been cast as Chris, Ashley Williams (How I Met Your Mother), as Shanann and Brooke Smith (Bates Motel, Ray Donovan) as FBI agent Tammy Lee. Sony Pictures Television is producing the film for Lifetime.

Image zoom From left: Ashley Williams; Sean Kleier; Brooke Smith Paul Archuleta/FilmMagic; Mike Pont/Getty; Amanda Edwards/WireImage

On Aug. 13, 2018, Chris killed his 15-weeks-pregnant wife and their two young daughters. He first strangled Shanann, then, with her body in the back of his truck, he drove to a remote oil work site with his sleeping daughters — Bella, 4, and Celeste, 3 — in the backseat.

Before burying Shanann in a shallow grave, Watts said he smothered Celeste in the backseat, right next to Bella. After dumping Celeste’s body in an oil tank, he returned to smother Bella, who begged for her life. He then stashed her body in another oil tank.

Image zoom Chris Watts RJ Sangosti/The Denver Post/Getty Images

Image zoom The Watts family Facebook

At the time of the murders, Watts was having an affair with a co-worker, Nichol Kessinger. Kessinger cooperated with police and said she thought Watts was separated while they were dating.

Watts didn’t immediately admit to his actions. According to an arrest affidavit obtained by PEOPLE, Chris allegedly said that after he told Shanann he wanted to split up when she got back from a work trip, he saw her strangling Celeste while Bella lay “blue” and apparently lifeless on her bed. In response, Chris allegedly claimed he “went into a rage” and strangled Shanann.

But authorities didn’t buy his shocking explanation. As the case headed for trial, Chris, now 34, pleaded guilty to all three killings. He is currently serving five life sentences without the possibility of parole.