Colorado is still haunted by the brutal slaying of a suburban Denver mom and her two young daughters at the hands of their seemingly nice dad.

According to a newly released interview given by Chris Watts to police in prison, the 33-year-old strangled his pregnant wife in their bed before driving her body and their two daughters to a worksite, where he smothered the children with a blanket. Watts made the statements during authorities’ prison visit on Feb. 18, three months after he was sentenced to life in prison.

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The shocking crime is the subject of a new documentary on Investigation Discovery (ID) titled “Family Man, Family Murderer: An ID Murder Mystery” airing June 2.

The mini-series features interviews with those familiar with the tragedy and experts who have covered the case extensively. It also highlights body camera footage from the Frederick Police Department, as well as new details from the investigation following Watts’ jailhouse confession.

Steve Wrenn, the Deputy District Attorney for Weld County who was interviewed for the special, told Fox News those who handled the case are still attempting to make sense of it.

“Police officers, first responders, prosecutors, defense attorneys — we operate in a world where we see bad people do bad things on a somewhat daily basis,” said Wrenn. “This took it to a level that I don’t think a lot of people are still able to get their heads around it. It’s impacted the way we go about our daily lives and how we interact with our families, how we are able to do our jobs sometimes.”

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“The ripple of one crime like this has been phenomenal,” Wrenn continued. “The first responders that had to remove the children from the oil tanks — they’ll never be the same. Some of the investigators I know had struggled to return to their jobs and go about investigations the same way.”

The terrifying turn of events first occurred with the disappearance of Shanann Watts and the children in August. But within days, the patriarch was arrested and then pleaded guilty in exchange for prosecutors not seeking the death penalty. At the time, Watts didn’t provide a full account of what occurred or his motives.

Watts previously told investigators he killed the 34-year-old, who was pregnant with their son Nico after she allegedly strangled their daughters, 4-year-old Bella and 3-year-old Celeste. However, he later admitted that was a lie and he was solely responsible for the murders.

According to Watts, he strangled Shanann in their bed last August after he told her their marriage was over and she allegedly said he would never see their children again. He said his wife suspected he was having an affair, which was true. However, Watts claimed he didn’t tell her about the ongoing relationship with a co-worker before killing her.

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When authorities speculated Watts wanted a fresh start with his mistress, he told investigators in February that the woman never asked him to get rid of his family. Still, the relationship may have “contributed” to his actions.

Wrenn said the first responders weren’t the only ones shaken by Watts’ actions.

“[Also] those who had to attend the autopsies the next day,” said Wrenn. “Those of us who had to sit and be frustrated by the fact that Chris Watts refused to tell us the truth in the initial interview. We knew he was lying, we knew he was involved. We wanted to find those kids and find Shanann. We knew he held the answers to those questions. His denials and the arrogance contained within those denials — I don’t know if I’ve ever been more frustrated in my life watching something take place.”

Watts confessed that after he strangled Shanann, Bella came into the couples’ bedroom clutching a blanket, asking what was wrong with her mother. Watts responded the matriarch wasn’t feeling well. Bella then watched as Watts wrapped the body in a bed sheet and started crying when he pulled it down the stairs of their home. Watts said he put the corpse on the floor of his truck’s back set. Celeste then woke up from the commotion.

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While Watts claimed he had no plans for his daughters, he still put the girls into the backseat of his truck where they occasionally napped on each other’s laps as he drove. Each child had their own blanket and Celeste also brought along a stuffed animal.

Watts drove to about 40 miles east of the family’s home in Frederick to an oil worksite where he worked as an operator for an oil and gas producer. Watts told police he pulled Shanann’s body from the truck while the girls asked, “What are you doing to mommy?”

Watts then said he went back to the truck and used Celeste’s blanket to smother her as Bella watched from a seat beside her sister. Then, he put Celeste’s body inside an oil tank. He then returned to the truck and smothered Bella using the same blanket. He told police Bella’s last words were “Daddy, no!” as she struggled under the blanket. He then put her body inside another oil tank and buried Shanann's body nearby.

Watts alleged he did not plan to murder his family.

“I do agree that this crime can only be committed by a sociopath,” said Wrenn. “There’s no other possible explanation.”

Wrenn insisted that despite Watts’ tell-all to investigators, we may never truly know why he was willing to slaughter his entire family.

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“When he gave that post-conviction prison interview to the FBI, I think we do get some glimpses into the why,” he explained. “But when you engage in an act that his so horrific and is so far removed from anything the average person ever contemplates doing to their own children, the why is going to be so elusive. It’s nonsensical. It’s so contrary to everything we know about human nature. And for that reason, the why is never going to be satisfying.”

“I’m speculating, but based on his own words [he spoke out] because there was a sense of… the cleansing of the conscious,” he continued. “He was trying to come to grips with his future and his faith… Sometimes that happens in a case… there is a desire to let the truth come out. I don’t know if everything he said in that interview was the truth. I don’t know if we’ll ever know [why]. But I think it was a lot closer than what we had before.”

The Denver Post reported Watts was charged Aug. 20 with multiple counts of first-degree murder, unlawful termination of pregnancy and tampering with a deceased human body. In November, a Colorado judge sentenced Watts to three consecutive life terms in prison, representing each victim.

Watts told investigators that he pleaded guilty to avoid a lengthy trial playing out before family. He also insisted he didn’t feel pressured by his attorneys to make an agreement with prosecutors. Watts also claimed he read the Bible for the first time in prison and he writes scriptures every day to send his parents. He then alleged to keeping photos of his slain family in his cell and talks to them “every morning and every night.”

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“The crime affected a lot of people,” said Wrenn. "Locally and nationally. Our initial instinct is to want to understand the why. I don’t think a documentary is capable of providing that answer, but maybe it will shed some light on the bigger picture… the factual backdrop in which such a horrific act can be committed."

“When you looked into his day-to-day activities, the guy would get up, go to work, go home, play with his kids, talk on the phone with his buddies about fantasy football, send text messages throughout the day to his wife about their weekend plans — we can all relate to that lifestyle,” he added. “That’s different from what we normally see in criminal investigations. It’s hard to relate to the people we are investigating because their lives often look so different from ours. Chris Watts’ life didn’t look that much different from the people who were investigating it.”

"Family Man, Family Murderer: An ID Murder Mystery" airs Sunday, June 2 at 10 p.m. on ID. The Associated Press contributed to this report.