Watts is accused of killing his wife, Shanann, and his two young daughters, Bella and Celeste.
Watts appeared in court Tuesday and pleaded guilty to all nine counts against him, including five counts of first-degree murder, one count of unlawful termination of a pregnancy, and three counts of tampering with a deceased human body.
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.
Watts reported his wife and their girls, 4-year-old Bella and 3-year-old Celeste, missing August 13 from their home in Frederick, a town about 30 miles north of Denver. The three bodies were found on property near Roggen owned by Anadarko Petroleum Co., where Watts worked as an operator until August 15.
The girls' bodies were found in oil barrels and Shanann's body was found in a shallow grave nearby.
Investigators discovered Watts was "actively involved in an affair with a co-worker", which he had denied during an earlier interview.
Family friend Ashley Bell said he did not understand why Watts killed his family, describing him as a loving father and his wife as "pretty happy" at the time of her death.
However, in a second interview with police, Watts told police he looked at the baby monitor screen and saw Shanann strangling their daughter Celeste and that he saw their older daughter, Bella, blue and "sprawled" out on her bed, according to the affidavit.
District Attorney Michael Rourke told the court Shannan Watts' family "were strongly in favour" of coming to a resolution, which didn't see the 33-year-old sentenced to death, Fox 31 Denver reported.
Rourke said Tuesday that investigators never believed that Watts was being entirely truthful.
'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. "I do not want to be in a position of making the choice to take his, '" Rourke said.
"That, to me, was the most important consideration in deciding how to proceed with this case", Mr Rourke said.
Rourke said he hoped the agreement would bring some measure of closure for the family, who were present during the court hearing and the press conference.
"Shanann Watts" mother, Sandra Rzucek, told Rourke " '(Watts) made the choice to take their lives, ' " the district attorney said, the Denver Post reported. Rourke said he was "sick" and "saddened' over the case". The spotlight shines squarely on him, ' he said.
'No one wins today.
Image: Shanann and Christopher Watts. I never wanted to have to stand up and have a press conference like this.