In exchange for Chris Watts' guilty plea, the death penalty will not be considered, the Weld County District Attorney's office said.
Watts acknowledged strangling his wife, Shanann, 34, and their daughters, Bella, 4, and Celeste, 3, and dumping their bodies in an oil field belonging to Anadarko Petroleum, where Watts had worked until he was arrested in the case, according to Denver 7 News.
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.
He could be heard sniffing and trembled each time he said "guilty" in response to each charge read against him by the judge.
"They were very strongly in favor of a resolution in this case short of the death penalty", Rourke said. The victims' family agreed to those terms, the district attorney's office added.
"Sandra said it best when she said: 'He made that choice to take their lives". The bodies of Bella and Celeste were later found nearby in an oil tank.
The agreement also required Watts to plead guilty to unlawful termination of Shanann Watts' pregnancy, a felony in Colorado.
Watts' family had all flown out to Colorado in order to be in court today to support him. "'I do not want to be in a position of making the choice to take his'".
"I can only say that I hope there is a sense of closure", Weld County District Attorney Michael Rourke said following the hearing.
As part of the sentencing agreement, Watts will spend the rest of his life in prison for the first-degree murder charges.
'I don't know how I could have sat in Sandy's kitchen and asked her to commit the next 25 years of her life to the criminal justice system without any assurance that the sentence would ever actually be imposed, ' he said.
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.
Investigators never believed Watts' stories, Rourke said.
Asked if a motive has been determined in the case, Rourke said that investigators believe they have a "partial motive" and Rourke said he would have more to say about that following the sentencing, which is scheduled for November 19.