A Colorado father who made national news after murdering his pregnant wife and their two young daughters—then dumping their bodies in an oil field where he worked—has been sentenced to life in prison.

Chris Watts pleaded guilty to the slayings earlier this month to avoid the death penalty. As part of the agreement, the 33-year-old will serve life without parole for nine criminal counts, including unlawful termination of pregnancy for the death of his unborn son, Nico.

Watts’ wife of six years, 34-year-old Shanann Watts, and their daughters Bella, 4, and Celeste, 3, were reported missing from their Denver-area home on Aug. 13, hours after Shanann returned from a business trip in Arizona.

Their bodies were discovered three days later: Shanann in a shallow grave and the girls each stuffed into separate tanks, submerged in oil for days.

During the sentencing on Monday, Weld County prosecutor Michael Rourke alluded to the only known motive in the killings—that Watts was having an affair with a coworker and wanted to start a new life without his family.

Watts bowed his head at the table where he sat flanked by his attorneys. He bounced his leg as the judge, who described the case as “the most inhumane and vicious crime” he’s seen in his career, addressed him.

Frank Rzucek, Shanann’s father, was the first to speak during the hearing, calling Watts a “heartless monster” who murdered his family before taking “them out like trash.”

“You disgust me,” Rzucek said at a podium, with Watts staring down behind him. “They were loving and caring people. You may have taken their bodies from me, but you will never take the love they had for me.”

“Prison is too good for you,” Rzucek added. “This is hard to say but may God have mercy on your soul.”

Shanann’s brother, Frank Rzucek Jr., and their mother, Sandy, also shared statements. Sandy said her family asked authorities not to pursue capital punishment against Watts. “Not only did you take the family of four, your family of four, you took your own life,” Sandy told the courtroom.

“I didn’t want death for you because that’s not my right. Your life is between you and God now and I pray that he has mercy for you,” Sandy said.

Cindy and Ronnie Watts, the killer’s parents, also stood in court as their attorney read a statement indicating they accepted their son’s plea deal. The words were an about-face from a recent Denver7 interview where they questioned the agreement.

The parents said they hope Watts will finally confess to exactly why he killed Shanann and his girls and provide answers to lingering questions.

Cindy Watts spoke directly to her son. “You were a good friend, brother, father and son. We have loved you from the beginning and we still love you now,” she said.

She turned around and addressed him, saying, “We forgive you, son.”

“ What must Bella, age 4, and Celeste, age 3, must have experienced or thought as their father—the one man on this planet who was supposed to nurture or protect them—was snuffing out their lives. ”

Rourke, speaking on behalf of the prosecution, revealed further details of the horrific crime. “The questions that have screamed out to anyone who will listen since Aug. 13, 2018, are why and how,” Rourke said.

“Why did this have to happen? How could a seemingly normal husband and father annihilate his entire family? For what?” Rourke told the court, before saying he doubted Watts would ever tell the truth about what happened.

“The defendant coldly and deliberately ended four lives, not in a fit of rage, not by way of accident, but in a calculated and sickening manner,” Rourke said.

Shanann’s body didn’t have any defensive wounds, Rourke said; the only marks found on her were fingernail bruising to the side of her neck. Meanwhile, little Bella and Celeste died of smothering.

“Even worse. What must Bella, age 4, and Celeste, age 3, must have experienced or thought as their father—the one man on this planet who was supposed to nurture or protect them—was snuffing out their lives,” Rourke said.

Bella fought for her life, Rourke said, and bit her tongue several times before she died. Celeste had no external injuries from the smothering.

“The defendant then methodically and calmly loaded their bodies into his work truck,” Rourke said, adding that Watts “ensured that they would not be together, even in death.”

Watts dumped Shanann in a “shallow grave,” before shoving Bella and Celeste through a hatch at the top of the oil tanks. The openings were only 8 inches in diameter.

“These were his daughters,” the district attorney said, adding that coworkers told police that Watts was “acting completely normally.”

“ Shanann repeatedly texted her husband in the days before the murder, desperately trying to save their marriage ... She sent him self-help and relationship counseling books, one of which police discovered in the trash. ”

“It was a normal work day, even as [his] daughters sank in the oil not far away from him,” Rourke said.

Shanann repeatedly texted her husband in the days before the murder, desperately trying to save their marriage, Rourke added. She sent him self-help and relationship counseling books, one of which police discovered in the trash.

All the while, Watts was busy scouring the Internet for vacation spots to take his new girlfriend, whom he took to car museums and sand dunes while Shanann and their kids visited family in North Carolina over the summer.

The morning his family vanished, Rourke said, he called his daughters’ school to disenroll them, as well as a realtor to discuss selling his house. “And he texted with his girlfriend about their future,” Rourke continued.

“If he was this happy and wanted a new start, get a divorce. You don’t annihilate your family and throw them away like garbage,” Rourke fumed. “Why did Nico, Celeste, Bella and Shanann have to lose their lives in order for him to get what he wanted?”

Through one of his attorneys, Watts said he was “devastated” by what happened and “is sincerely sorry for all of this.” He declined to speak to the courtroom directly.

The day after his family vanished, Watts gave a bizarre interview to Denver7, pleading for their return—an interview Rourke described as “emotionless.”

Watts said Shanann was at their Frederick home when he left for work at Anadarko Petroleum Corporation around 5:30 a.m. Asked if the couple had an argument, Watts replied, “It wasn’t like an argument. We had an emotional conversation. I’ll leave it at that.”

“It was tearing me apart last night,” Watts said. “I want everybody to just come home. Wherever they’re at, just come home. That’s what I want.”

Police weren’t alone in their suspicions of Watts. Shanann’s friend Nickole Atkinson dropped Shanann off at home around 2 a.m. the day she disappeared, after their flight from Arizona had experienced delays. Atkinson would soon report Shanann missing.

That morning, Atkinson visited the Watts residence when she couldn’t reach Shanann, who had missed a morning doctor’s appointment. Shanann’s car was in the garage, Atkinson told police. Worried Shanann was sick, Atkinson tried to open their front door but a latch barred her from getting inside. She immediately phoned Chris.

“He just kept saying that he didn’t know where she was and that she was on a playdate,” Atkinson recalled. “But he couldn’t give us the name of the friend. I knew he had something to do with it the day I was at his house with him, but I didn’t want to think that.”

Police arrested Watts on suspicion of first-degree murder on Aug. 15—one day after his unemotional TV appearance. On Aug. 16, cops discovered the body of Shanann, who was 15 weeks pregnant, at the Anadarko oil field where Watts worked. The children’s bodies were discovered nearby, stuffed inside oil tanks.

According to an arrest affidavit, Watts was having an affair with an unnamed coworker and broached separating from his wife before he killed her.

“Chris said he woke up around 5:00 AM and began talking to Shanann about marital separation and informed her he wanted to initiate the separation. Chris stated it was a civil conversation and they were not arguing but were emotional,” the document states.

Watts told police he flew into a rage and strangled Shanann, because she had strangled their children moments after they discussed breaking up. He claimed he saw Shanann murdering their kids when he looked at a baby monitor on his wife’s night stand.

The killer then, according to the affidavit, drove the bodies to his work site. He was spotted on a neighbor’s security camera backing his truck up to his garage around 5:27 a.m., cops said.

Investigators deployed a drone in the oil field and found a sheet matching the couple’s bedding, some of which was also discovered in the trash at the Watts home.

News of Watts’ heinous crime shocked his friends and family.

As The Daily Beast reported, Watts and Shanann appeared to have a picture-perfect life. They’d moved from North Carolina to Colorado, eventually buying a big house. Shanann’s job with a multi-level marketing venture allowed them to travel for free to Las Vegas and San Diego.

On Facebook, Shanann routinely shared loving tributes to her husband. On Watts’ birthday last May, Shanann wrote, “Today I celebrate you! Chris, you are absolutely the BEST thing that ever happened to me in 2010!”

“You work your ass off, you’re an amazing husband and an even better dad!” she continued. “You are the blessing I’ve been looking for my whole life!”

Still, friends said Shanann suspected Chris was cheating on her.

“He wasn’t being the loving Chris that he normally was,” Atkinson told ABC News. “He wasn’t touching or hugging or doing stuff like that. He wasn’t being as attentive to the girls as he normally is.”

Watts’ alleged mistress, former Anadarko coworker Nichol Kessinger, spoke out last week to The Denver Post as his sentencing loomed, saying Watts lied to her during their relationship, which she says lasted less than two months.

Kessinger told the Post she began dating Watts in July, believing he was close to finalizing a divorce with Shanann. But Kessinger would learn, after his family’s disappearance made news, that Watts never actually started divorce proceedings.

She said she went to police before Watts was arrested. "We had just met,” the 30-year-old told the newspaper. “I barely knew him.”

Watts didn’t wear a wedding ring, Kessinger recalled. She said he was “very soft spoken” and “appeared to be a good listener.” When they met, he allegedly told Kessinger he was separated, soon to be divorced and had two daughters.

Kessinger said she saw Watts four to five times a week, and that he asked her to help him find an apartment that would be good for him and his kids.

Watts texted Kessinger throughout the day on Aug. 13, as friends desperately searched for Shanann, Bella and Celeste. Around 3:45 p.m., Watts sent Kessinger a message saying his family was “gone,” after Shanann took the girls on a playdate.

That night, Watts changed his story about his supposed divorce, as Kessinger questioned him in phone calls and over text messages.

“It got to a point that he was telling me so many lies that I eventually told him that I did not want to speak to him again until his family was found,” Kessinger told the Post.

“He’s a liar,” she added. “He lied about everything.”