GREELEY, Colo. (Reuters) - A Colorado man pleaded guilty on Tuesday to charges of murdering his pregnant wife and two small daughters and dumping their bodies in an oil field in an agreement that will spare him the death penalty.

Christopher Watts, 33, admitted in Weld County District Court to strangling his wife, Shanann, 34, and the couple’s two daughters, Celeste, 3, and Bella, 4, in August at the family’s home in Frederick, about 30 miles (48 km) north of Denver.

Watts’ voice quavered slightly as he entered the guilty pleas before Judge Marcelo Kopcow. He was handcuffed and dressed in an orange jail outfit and wore a bullet-proof vest.

Authorities declined to say why Watts was given the vest.

Watts pleaded guilty to charges of first-degree murder in the deaths of his wife and daughters and allegations that he killed the girls while in a position of trust. He also pleaded guilty to unlawfully terminating a pregnancy and tampering with the bodies of the three victims.

Under Colorado law, a first-degree murder conviction carries a mandatory life sentence without the possibility of parole.

“He deserves a life sentence for each and every act,” Weld County District Attorney Michael Rourke said at a news conference on Tuesday.

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Watts had faced the possibility of the death penalty if convicted, but under his plea agreement prosecutors pledged to not seek the death penalty, Steve Wrenn, chief deputy district attorney for Weld County, told the judge.

Rourke said he traveled to North Carolina, where Shanann Watts’ family lives, to consult with them before entering into the plea deal.

‘FLAT OUT LIE’

After Shanann Watts and the two girls were reported missing in August, Christopher Watts went on multiple Denver television stations pleading for their safe return. The following day, Aug. 15, he was arrested for the murders.

Watts initially told police that he strangled his wife in a rage because, after the couple had argued, she killed their two girls. The suggestion that Shanann Watts killed the girls was a “flat out lie,” Rourke said on Tuesday.

Prosecutors have not said what motivated Watts to kill his them.

Watts told detectives that he was having an affair, according to an arrest warrant affidavit, and that he had loaded the bodies of his wife and daughters into his truck and taken them to an oil field. The bodies were found the week Watts was arrested.

Shanann Watts was 15 weeks pregnant.