By Crimesider Staff CBS/AP August 20, 2018, 5:15 PM Shanann Watts' body was found in shallow grave near oil tank, prosecutors say

FREDERICK, Colo. — The body of a pregnant Colorado mother was found in a shallow grave near an oil tank where her daughter's bodies were submerged for days, prosecutors said in court documents released Monday. Autopsies were completed Friday on Shanann Watts, 34, and her daughters, 4-year-old Bella and 3-year-old Celeste.

The cause of their deaths has not been made public. A defense motion seeking the DNA samples from the young girls' necks suggested that they may have been strangled.

Christopher Watts, 33, is expected to be formally charged with killing his wife and children on Monday afternoon and an affidavit was expected to be released that could shed more light on the case against him. Watts remains jailed in protective custody. Officials are scheduled to hold a press conference at 6 p.m. ET Monday on the investigation.

Shanann Watts and her two daughters were reported missing since Monday.

CBS Denver

Police arrested Christopher Watts late Wednesday on suspicion of killing his wife and children. Their bodies were found on Thursday on property owned by Anadarko Petroleum, one of Colorado's largest oil and gas drillers, where Watts worked as an operator. Court documents filed by defense lawyer James Merson said the girls had been submerged in crude oil for four days.

Shanann Watts' body was found in a shallow grave, according to a prosecution motion filed last week asking a judge to deny a request by the defense for an expert to be present at the autopsies. A judge later approved the prosecution's motion and disallowed the presence of the defense expert. The Weld County Coroner said "time is of the essence" in performing the autopsies given the length of time the girls' bodies were submerged, the document says.

The couple had financial problems and filed for bankruptcy in 2015, but so far investigators have not revealed a motive for the killings.

A day before his Wednesday arrest, Watts had issued a televised plea for the return of his wife and daughters.

Outside the family's home in Frederick, north of Denver, a memorial of stuffed animals, balloons, flowers and messages grew and a candlelight vigil drew dozens of people Friday night.

"This is to celebrate, mourn and get closure for a family that didn't deserve this," said vigil organizer Kelley Trippy. "This is a horrible, horrible, horrible story. It's affected us all whether you do know them or don't know them."

Christine Gentert said a prayer, adding that she wanted Shanann Watts to be remembered for her smile and her love for others.

"I don't want the horror to replace how beautiful she was," Gentert said.

Ashley Bell, a friend of Shanann Watts, said Shanann had planned a party Saturday to reveal the gender of her baby. Frankie Rzucek said his sister planned to name her baby boy Niko.

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