Police believe an Arizona mother of nine smothered her 6-day-old baby to death because she thought she had too many children already.

Nina Koistinen, 36, was charged with first-degree murder after Phoenix authorities say she “admitted to purposely smothering the baby to death,” ABC 15 reported.

The child, Maya Koistinen, died on April 8. The father, Bradley Koistinen, called 911 at about 6:45 a.m. after he said he found Maya lying next to her mother, not breathing, KPHO reported. Maya died at the hospital, and an autopsy of the baby showed signs that she might have suffocated.

Koistinen initially told investigators that she fell asleep while nursing the infant, but during a second interview on April 25, she “admitted to purposely smothering the baby to death,” according to documents obtained by ABC 15.

She claims she did it because she was jealous that husband, Bradley, was giving too much attention to the victim. She also allegedly claimed that she already had too many kids.

According to Child Protective Services records, Nina Koistinen has made comments in the past about “wanting to smother” some of her kids, the Phoenix New Times reported. Records also state that after a car crash that appeared to be intentional, Koistinen said she wanted her children to go to heaven.

Bradley Koistinen maintains his wife is innocent.

“She has been the greatest mother,” he said at her first court appearance on Friday. “We’ve been married 15 years … She never once has she hurt any of our kids.”

He noted that his wife suffers from bipolar disorder, schizophrenia and depression.

Read more: Huffington Post