WEST VALLEY CITY — A West Valley mother accused of killing her 4-year-old daughter caused numerous extensive injuries to the young girl, including nearly severing her shoulder, according to charging documents.

Graphic and disturbing new details were revealed Wednesday in documents filed in 3rd District Court charging Nicole Terri Lester, 29, with aggravated murder, a first-degree felony.

On Dec. 31, police were called to 4502 W. Losee Drive (4355 South) about 5 a.m. after Lester called 911 to report, “I just killed my daughter,” according to charging documents.

Officers said they arrived to find Lester outside her house saying, “I need to be arrested now.”

In the basement, 4-year-old Lainey Vos was found with “multiple lacerations to her body,” according to charging documents. “It appeared her shoulder and wrist were partially severed. There were multiple deep lacerations to her chest centered on her heart.”

A “sharp, bloody ceramic kitchen knife” was recovered from the house, according to police.

Detectives later looked at Lester’s internet search history on her cellphone and discovered that during the month of December the mother searched “numerous topics that involved breaking a neck, smashing a head with an ax, breaking bones with an ax, stab wounds to the chest, broken and cracked ribs, and also included medical diagrams of a child’s chest,” the charges state.

The search history also included photos and video interviews from murder cases that had received media attention, according to investigators.

An autopsy found Lainey suffered more than 30 cutting injuries, including numerous defensive wounds to her arms, hands and shoulders. The injuries to the girl’s chest were so deep and numerous that her “heart, lungs and even her spine had received cutting injuries,” according to the charges.

Prosecutors have requested that Lester be held without bail.

Lester was convicted of drug possession and possession of drug paraphernalia in 2012. She pleaded guilty to the charges, which were later dismissed after she successfully completed probation.

Also in 2012 she was charged with misdemeanor assault in a domestic violence incident, according to court records. The case was later dismissed due to witness issues.

In 2014, she pleaded guilty to assault in exchange for a second count of assault and a charge of domestic violence in the presence of a child being dismissed, according to court records. As part of her probation, she was ordered to undergo mental health and domestic violence evaluations.

In 2013 she pleaded guilty to disorderly conduct in a case that also involved domestic violence, according to court records. Lester was ordered to undergo a domestic violence evaluation at that time.

Correction: In an earlier version, police spelled the child’s first name as Laney. An obituary identifies her as Lainey.