Prosecutors have said they agreed not to seek the death penalty in exchange for Christopher Watts' guilty plea, after seeking approval from Shanann Watts' family.
Forensic pathologist Dr. Michael A. Burson's reports shed new light on Shannan's strangulation and how the girls' father smothered his children to death.
Shannan's body arrived at her Aug. 17 examination wearing a purple T-shirt, the clothes she had on when she was buried in a shallow grave by her husband.
Examiners reported finding possible patterned abrasions on Shannan's neck and on the left side of her face, while internal examination showed bruising of the neck consistent with someone being strangled.
Shannan's 3- and 4-year-old daughters, who were pulled out of an oil tank by investigators, had a variety of toxins in their system, a symptom of body decomposition and being submerged in oil for several days.
Celeste's body arrived at the examiner's office wearing a pink and black T-shirt and a diaper; the body of her older sister, Bella, still had on her pink pajama top with hearts and butterflies. Both died after being smothered, examiners found.
Watts had pleaded guilty to three charges of murder in the deaths of his wife and their young daughters. He also pleaded guilty on Nov. 6 to two counts of killing a child, one count of unlawful termination of a pregnancy and three counts of tampering with a deceased human body.
The 33-year-old will not be eligible for parole.
A friend asked police to check on Shanann on Aug. 13 after not being able to reach her and growing concerned that the 34-year-old expectant mother had missed a doctor's appointment. Officers initially handled the search and soon sought support from Colorado investigators and the FBI.
Meanwhile, Christopher Watts spoke to local television reporters from the front porch of the family's home in Frederick, a small town on the plains north of Denver where drilling rigs and oil wells surround booming subdivisions. Watts pleaded for his family's safe return, telling reporters their house felt empty without 4-year-old Bella and 3-year-old Celeste watching cartoons or running to greet him at the door.
Within days, he was arrested and charged with killing his family.
Court records revealed that Watts acknowledged to police that he killed his wife. Watts told investigators that he strangled her in "a rage" when he discovered she had killed their daughters after he sought a separation.
Prosecutors have since called his account "a flat-out lie."
Police learned that Christopher Watts was having an affair with a co-worker. He had denied that before being arrested.
The girls' bodies were found on property owned by the company Watts worked for until his arrest. Shanann's body was found buried nearby in a shallow grave.
The killings captured the attention of media across the country and became the focus of true crime blogs and online video channels, aided by dozens of family photos and videos that Shanann shared on social media showing the smiling couple spending time with their children.
But courts records showed the couple's lifestyle caused financial strain at times. They filed for bankruptcy in June 2015, six months after Christopher was hired as an operator for the large oil and gas driller Anadarko Petroleum at an annual salary of about $61,500. At the time, Shanann was working in a children's hospital call center for $18 per hour.
They reported total earnings of $90,000 in 2014, but $70,000 in unsecured claims along with a mortgage of nearly $3,000. The claims included thousands of dollars in credit card debt, some student loans and medical bills.
The Associated Press contributed to this report.
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