The 23-year-old woman who was one of two people accused of stabbing to death and dismembering a man and a teenage girl in August 2017 pleaded guilty Thursday morning in Missoula County District Court.

Tiffanie Pierce was charged in the killings of Jackson Wiles, 24, and Marilyn Pickett, 15, who police found dismembered and partially dissolved in tubs of chemicals. Her plea agreement calls for life in prison with no restrictions on her eligibility to seek parole. Her co-defendant in the case, Augustus Standingrock, 26, pleaded guilty in December. His plea agreement recommends a life sentence in which he is eligible for parole.

As Judge James Wheelis asked Pierce procedural questions before she entered her plea, Pierce became emotional, put her hands to her face and asked for a break just eight minutes into the hearing. In previous hearings, she had seemed especially at ease considering the charges, smiling at those in the crowd and sometimes laughing with law enforcement.

Pierce had been set to stand two trials — one for a home invasion on Montana Street, where she was accused of attacking someone with a knife weeks before the killings. She faced a separate trial for the killings of Wiles and Pickett, and as recently as last month was renegotiating trial dates. But the recent death of a key witness in the state's case, Kyle Belz, had accelerated the case to Thursday's plea agreement. The coroner ruled Belz's death a suicide, Missoula County Attorney Kirsten Pabst said.

Belz and Pierce were friends and roommates, sharing the home where the killings took place. Charging documents state Belz had seen Pierce and Standingrock come up from the basement covered in blood. He had not reported the incident to authorities, but cooperated with them after the arrest. 

The plea agreement called for Pierce’s guilty pleas on two of the five counts: attempted deliberate homicide and accountability to deliberate homicide.

The first count stems from the incident, referred to as "the Montana Street case," weeks before the killings. In that case Pierce reportedly broke into a Montana Street home and stabbed a woman, who was only watching the house for a friend. Pierce had also faced an aggravated burglary charge in that case for demanding money and a phone from a man who was also in the  home. 

As she read a prepared statement in court to establish the facts for each charge, Pierce paused to make her own clarification. 

"I didn't stab her, I slashed her, with my knife," she said, referring to the Montana Street case. "Here it says stabbed, I didn't stab her."

"One of those was across the throat?" Missoula Deputy County Attorney Jen Clark asked her later. 

"Probably," Pierce responded. "It was dark, I couldn't see."

The accountability charge to which she pleaded guilty follows the theory in the dismemberment case that Standingrock devised the killings of Pickett and Wiles, who authorities believe sexually assaulted someone close to Standingrock. 

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During his own change of plea hearing in December, Standingrock spoke in open court about fatally stabbing Wiles, then passing the knife to Pierce, saying he knew she would kill Pickett. 

Pierce's accountability charge assigns her conviction to Pickett's death, although she admitted only to preventing Pickett from leaving her basement on that day in August 2017. 

"My reaction, initially, was based out of fear and that led to the death of two people at my home," she said. 

"And you aided Augustus Standingrock in the death of Marilyn Pickett, would you agree you did that by tackling Marilyn when she tried to run and holding her?" Clark asked.

"I didn't tackle her, I prevented her from leaving, yes."

Even without measures barring her from seeking parole, Wheelis said Pierce won't be up for the state parole board for 30 years after her initial arrest. She will be 53 years old.

No date was scheduled Thursday for Pierce's sentencing.

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