A Colorado father was sentenced to three consecutive lifetimes in prison after a prosecutor detailed for the first time how Christopher Watts planned the August murders of his pregnant wife and two young daughters — apparently in the hope of starting a new life with his girlfriend.

But neither prosecutors nor the surviving relatives of Shanann, Bella and Celeste Watts who spoke at Monday’s hearing expected to ever understand how “a seemingly normal person [could] annihilate his entire family” and then methodically cover his tracks, as Weld County District Attorney Michael Rourke put it.

“You buried my daughter Shanann in a shallow grave, and then you put Bella and Celeste in huge containers with crude oil, you heartless monster,” Frank Rzucek told the court as his son-in-law sat behind him clenching and unclenching his jaw, having already pleaded guilty to the murders.

“I hope you see that every time you close your eyes at night,” he said.

Three months earlier on Aug. 13, Christopher Watts at first seemed as much a victim as anyone when his wife and daughters — 3 and 4 years old — disappeared.

From his doorstep in Frederick, the 33-year-old oil-field operator told reporters that he had rushed home from work upon hearing that Shanann’s friends couldn’t find her or reach her. “In my heart, I believe she is somewhere, and I hope she is safe,” he told Fox 31 as police searched the house behind him.

The illusion held up for a day or so, at least on TV. A neighbor down the street recalled how Christopher Watts used to play with the girls in a wagon, and his social media feeds were full of love odes to his family and the “little peanut” growing in Shanann’s womb, to be named Nico.

But investigators were immediately suspicious after finding Shanann’s wallet and keys still in the house.

A day after the disappearance, a woman named Nichol Kessinger contacted the sheriff’s office after seeing Watts on the news, the Denver Post reported. She told investigators that she had been dating him for several weeks, under the impression that he was in the process of finalizing a divorce and moving out with his daughters.

“He lied about everything,” Kessinger later told the Denver Post.

At Monday’s hearing, the district attorney alleged that Shanann had been trying to save the marriage for weeks — texting her husband and buying self-help books as he shopped for jewelry and vacation spots to take his “new love.”

“His motive was simple, your honor,” Rourke said. “He had a desire for a fresh start.”

Police arrested Watts after interviewing Kessinger and soon announced that he had confessed to killing Shanann in “a rage” — claiming he had walked in on his wife as she was strangling their two girls, too late to save them.

An investigation proved that was a lie, too, Rourke said. “The man seated to my right smothered his daughters,” he said as Watts looked down at his handcuffs, one leg occasionally shaking beneath the table. An autopsy found a cut in Bella’s mouth, he said, suggesting that “she fought back for her life” and bit her tongue before she died.

Watts had been home with the girls while Shanann was out of town that weekend. He killed his wife shortly after she returned from the airport early on a Monday morning.

A bruise in the shape of a finger mark on her neck told investigators that Watts had strangled her slowly and without resistance, Rourke told the court. “The horror she felt as the man she loved wrapped his hands around her throat and choked the life out of her must have been unimaginable,” he said.

Besides pleading guilty this month to all three murders and unlawful termination of a pregnancy, Watts admitted to tampering with their bodies.

On Monday, Rourke described how surveillance cameras showed Watts going back and forth between the house and his pickup in the darkness that morning — loading up the corpses before he drove to a company oil field “to secrete away his family in a place he hoped they’d never be found."

He dug a hole for Shanann and stuffed each of his daughters into a separate tank full of crude oil. Bella had to be shoved through the eight-inch hatch, Rourke said, leaving a tuft of blond hair on the side that investigators in hazmat suits would later discover.

And when he had done all that, Rourke said, Watts contacted a real estate agent to put the house on the market.

Cynthia and Ronnie Watts openly doubted that their son had really done all these things — even after he pleaded guilty to it all Nov. 6 in a deal that spared him the death penalty.

But on Monday, as the couple addressed the court and their son, they asked only that Watts one day explain himself.

“We love you, and we forgive you, son,” Cynthia Watts said, turning from the podium to look at him, though he still didn’t raise his eyes. “We are forced to question everything. We still don’t have all the answers, and I hope one day, Chris, you can help us.”

Watts said only two words at the hearing — “No, sir,” when Judge Marcelo Kopcow asked whether he had anything to say.

His in-laws, on the other hand, had much to say to him before he was escorted away to spend the rest of his life in prison. Shanann’s parents had urged prosecutors to spare Watts the death penalty, which they do not believe is moral.

“Our Shanann loved you with all her heart. Your children loved you to the moon and back,” Sandra Rzucek said, still holding her composure through the first half of her speech.

She lost it as she recalled the title of a song Bella sang: “Daddy You’re My Hero.”

“I have no idea who gave you the idea you have the right to take their lives,” Rzucek said, sobbing. “I didn’t want death for you, because that’s not my right."

Read more:

‘The kids are my life,’ a dad said of his missing family. Then he was charged with killing them.

He said he killed his wife after she strangled their daughters. Prosecutors say he killed them all.