According to the criminal complaint, per KSTP, Autumn's step-mom told officers the girl had said she was going to take a shower; when she checked on her 40 minutes later she found her floating face down in the water.
Autumn's father said he was woken by his partner's screams, and saw his daughter lying on the floor beside her.
After first responders unsuccessfully tried to revive the child, officers on the scene noted Autumn looked "extremely frail and thin", and that she had cuts and "pin-like" marks on her forehead.
Based on the condition of her body, officers determined she had been dead for some time.
The following day, child protective services interviewed Autumn's siblings. Her 6-year-old brother told them his parents would use a brown belt to tie Autumn up in a red sleeping bag whenever she wet herself or misbehaved, the complaint states. He said the sleeping bag would be moved to different rooms, or the bathtub.
He also said they sometimes tied her arms behind her back.
The morning Autumn died, her brother said he heard a loud bang from the bathroom when his parents were in there with her.
Autumn's 10-year-old sister also said she saw blood in the tub, and that Autumn wasn't breathing, according to the complaint.
They said their parents told them Autumn had fallen.
Autumn's biological mother Kelsey Kruse told investigators she hadn't seen her daughter since the end of January; she said she'd been denied parenting time over COVID concerns.
Both parents denied tying her in the sleeping bag; Sarah said she did not know why the child was losing hair, why she only weighed 45lbs or where her injuries came from, but admitted she never brought her to the doctor.
A medical examiner determined Autumn died from asphyxia injuries and blunt force trauma; she had a paired puncture wound on her head, bleeding in the abdomen and on the brain, and bruises to her hands and hips. The coroner ruled her death a homicide.
Brett and Sarah Hallow were arrested the day after the 911 call; this week they were each charged with second-degree murder and first-degree manslaughter.
Two days after Autumn's death, her mother wrote on Facebook: "You have given me and my family a permanent scar. You took something we will never get back. ... I hope your other children know what you did, and I hope they grow up knowing that their sister saved them."
In another post she wrote: "Your father kept you from me for several months, and he then took your life. I hope you know how much I tried to get you," the Star Tribune reported. "All of your siblings were lucky to have a sister like you."
A GoFundMe to raise money for funeral expenses has already raised $25k.