A woman accused of killing her 2-year-old son and hiding his body in the trunk of her car told detectives that the toddler died after falling from a high chair, according to an affidavit that includes transcripts of police interviews.

Summer ManyWhiteHorses, 31, was charged with deliberate homicide and tampering with evidence after her son James' body was discovered Sept. 5.

Cascade County Attorney Brant Light filed an affidavit in District Court on Monday outlining his argument for charging ManyWhiteHorses. The document builds the prosecutor's case on police interviews with the defendant and her relatives, arrest records and an X-ray of the child's body.

According to the affidavit, ManyWhiteHorses told detectives that her son fell from a high chair on the night of May 28 while she was watching television in another room.

"He fell and I jumped up and I went running over there and I grabbed him," she said, according to an interview transcribed in the affidavit.

"I hugged him and I laid by him on the couch and when I laid by him on the couch, like, his eyes rolled back ... I thought he'd be all right, and he went back to sleep," she said.

According to the affidavit, ManyWhiteHorses said she attempted CPR the next morning when she discovered James wasn't breathing, and she eventually wrapped her son's body in a blanket and placed it in her car trunk.

Prosecutors say ManyWhiteHorses and her 11-year-old daughter drove around the state throughout the summer and paid for food, gas, hotel rooms and alcohol with government checks meant to take care of James, who was autistic. ManyWhiteHorses is accused of keeping the toddler's body in the trunk during that time.

She was arrested and charged with DUI after crashing into a parked car in Great Falls on July 21. Police officers did not search the trunk, and the car was towed.

After her arrest, child welfare officials explored placing the daughter into state custody and were trying to determine the boy's whereabouts.

Police contacted ManyWhiteHorses after welfare officials filed a missing person's report Sept. 4. According to the affidavit, ManyWhiteHorses then revealed the location of the body, which has been sent to the state crime lab in Missoula.

Light said an X-ray taken by police shows the boy's head was turned 180 degrees — an injury the prosecutor thinks couldn't have come from a fall from a high chair.

ManyWhiteHorses is being held on $250,000 bail.