In court Tuesday, Watts took responsibility for all three deaths, pleading guilty to nine charges, including first-degree murder and unlawful termination of a pregnancy.
Investigators claimed in the documents that Watts admitted to police that he killed his wife.
Prosecutors say they dropped the possibility of the death penalty with the agreement of the victims' family.
At a news conference on Tuesday, Weld County District Attorney Michael Rourke called Watts' story "a flat-out lie" and said he deserved a life sentence for each of the nine counts to which he had pleaded guilty. "I was not willing to accept a concession above and beyond removing the death penalty". Shanann Watts' body was later discovered on the property of an oil and natural gas company that Christopher Watts had worked for.
It's alleged he drove their bodies to an oil site, and police said the girls' bodies were found in an oil tank while his wife's body was found in a shallow grave.
The district attorney said lawyers for Chris Watts reached out several weeks ago about making a deal.
He said he went off to work and only knew something was wrong when he was contacted later by her colleagues.
After his pregnant wife and two daughters disappeared, Watts stood on his porch in Colorado and told reporters how much he missed them.
Rourke said they may decide to testify when Christopher Watts is formally sentenced on November 19.
'I do not want to be in the position of choosing to take his'.
"I know that will never be fully realized because, obviously, the tragedy that sits before us today is the loss of four lovely lives".
Watts is represented by the Office of the Colorado State Public Defender, which does not comment on pending cases. Rourke said their wishes were the most compelling factor for him in reaching the plea agreement.
While both Rourke and CBI Director John Camper said they hope this provides some closure and sense of justice, they also recognized that nothing that happens in the courtroom can fix what happened in the Watts' Frederick home in August.
"The spotlight he tried to shine on Shanann, falsely, incorrectly.is now shined correctly on him", Rourke said.
According to People, the source said, Watts was furious at having to enter the guilty plea.
Rourke said investigators believe they have a partial motive for the slayings, but said he wouldn't give details until after Watts is sentenced.