Allegedly Abusive Man Charged with Killing Daughter, 6, During Custody Battle a Month Before Her Birthday

Last week, just as police in North Carolina were preparing to issue a statewide Amber Alert for a missing 6-year-old girl, officers on patrol say they spotted the child's father parked along the shoulder of a major roadway.

As they approached the vehicle, officers noticed Seth Pickering, 36, seated behind the wheel – and then they saw his daughter, Lila, dead in the back seat.

Authorities declined to release further details about Friday's homicide, including how the girl was killed. But they did reveal to PEOPLE that Lila's death followed a bitter, year-long custody battle between her estranged parents.

Pickering, who lives in Leicester, North Carolina, is charged with murder in Lila's death. He was arrested Friday night by deputies with the Buncombe County Sheriff's Office.

It was an hour earlier that authorities learned Lila had allegedly been taken by her father without permission. As officers were approaching Pickering's car, the necessary paperwork was being filed for an Amber Alert.

Lila's mother, Ashley Pickering, tells PEOPLE she had separated from her husband because he was both physically and mentally abusive. But she never imagined he would ever hurt their child.

"I never had a concern with him being with her, because he was an amazing father to her," Ashley says.

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Ashley says an autopsy on Lila's body will be performed Monday afternoon, but that detectives said her daughter had been fatally stabbed in the chest.

Seth allegedly took Lila – who would have turned 7 in October – from her home in Florida last year, moving with her to North Carolina and triggering the subsequent custody fight.

Seth allegedly kept Lila with him in North Carolina, but the state had recently placed Lila in protective custody, in a foster home, following Seth's alleged involvement in a physical fight with a neighbor, authorities said.

Lila was taken from the foster home before her death.

Ashley tells PEOPLE that her estranged husband was released from a psychiatric hospital two days before allegedly killing their daughter.

"He tried killing himself, and was committed," Ashley says. "He got out on Wednesday and he'd told a bunch of his friends he was going camping, to get off grid and clear his head."

"Me and him, we had our problems," she says. "But he loved that little girl."

A call to the Buncombe County Department of Health and Human Services, which includes protective children services, was not immediately returned.

It was not immediately clear if Seth has retained a defense attorney, and court records show he has yet to enter a plea to the murder charge.