January 11, 2018 10:57 AM

In chilling police video released this week, a 23-year-old Arizona woman can be seen allegedly confessing to smothering her 5-month-old daughter to death.

The footage was released by the Glendale Police Department, about a month before the start of Amber Sagarnaga’s murder trial.

Court records obtained by PEOPLE confirm that Sagarnaga was arrested last June, after the baby girl, named Mary, died.

She has been charged with murder and has pleaded not guilty.

Sagarnaga’s fiancé called 911 after discovering his daughter unresponsive, according to court filings.

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Sagarnaga was interrogated over two hours, and in the newly-released footage, can be heard telling police about the baby girl’s final moments.

Sagarnaga tells detectives she wanted to take a nap the afternoon of June 9, 2017. But she was unable to rest because Mary “wouldn’t stop crying,” she can be heard telling police in the video.

She continues to tell police she would often use blanket to quell the baby’s cries. But on June 9, she instead used a heavy, king-sized comforter.

Amber Sagarnaga
Maricopa County Sheriff's Office

She recalls for police how she placed the comforter over the baby’s head, holding it there longer than she usually would.

“I don’t know why,” she says in the footage. “I just didn’t take it off of her this time.”

Sagarnaga told police she slept for several hours afterwards.

Dispatchers instructed Sagarnaga’s fiancé as he tried resuscitating the child, but his efforts were unsuccessful.

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When police arrived on the scene, Sagarnaga allegedly seemed to be “lacking emotion,” according to online court filings.

Mary was pronounced dead later that evening. In charging documents, police noted that the deceased baby’s diaper was “soiled” and “appeared to have been on for more than a day.”

Sagarnaga’s other children, ages 1 and 2, were taken by the Department of Child Safety

Police allege that the day before Mary died, Sagarnaga struck the child with a bottle, leaving the baby’s lip lacerated.

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