Christopher Watts entered his plea Tuesday during a court hearing in Greeley.
Those who knew the Watts family have described a seemingly happy marriage possibly beset by rising tension, and his infidelity has drawn scrutiny: Authorities have said Chris was cheating with a co-worker when he murdered 34-year-old Shan'ann, Bella, 4, and Celeste, 3.
Watts' defense attorneys came to the prosecution weeks ago with proposals for plea deals, according to Rourke, though he doesn't know why they did.
Rourke said he and another prosecutor visited Shanann Watts' family in North Carolina last month to discuss the odds of a death penalty sentence being carried out.
"I can only say that I hope there is a sense of closure (for family members of the deceased)", Rourke told reporters.
"I know that will never be fully realized because, obviously, the tragedy that sits before us today is the loss of four attractive lives".
'That to me was the most important consideration in deciding how to proceed in this a case.
Watts is represented by the Office of the Colorado State Public Defender, which does not comment on pending cases.
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The Colorado Bureau of Investigations later said Shanann Watts and the girls were murdered inside their home.
Christopher Watts reached the plea deal Tuesday afternoon, CBS Denver reports.
At the time of her disappearance in August, according to an arrest affidavit, Christopher Watts initially told police officers he had just informed his wife that he wanted a separation. Watts told investigators he "went into a rage" and strangled his wife, then dumped all three bodies at the oil field owned by a company he had worked for.
"Shanann Watts" mother, Sandra Rzucek, told Rourke " '(Watts) made the choice to take their lives, ' " the district attorney said, the Denver Post reported.
Watts, 33, had been charged with murdering his wife of almost six years, Shanann, 34, and their two girls.
Rourke said Tuesday that investigators never believed that Watts was being entirely truthful.
'The spotlight that he tried to shine on Shanann, falsely and incorrectly - a flat out lie - has been corrected. "The spotlight shines directly where it belongs - on him", Rourke said.
Watts will receive his other sentencing terms on November 19, the date on which his status conference was previously scheduled. He will be sentenced to life in prison without parole.