It's believed a 15-year-old boy allegedly killed a 10-year-old girl after she went for a night-time walk to the shops, police say.
The Illinois boy was arrested over the weekend in relation to the death of 10-year-old Kiaya Campbell, according to the Thornton Police Department.
The teenager, whose name has not been released because he is a minor, was booked into the Adams County Juvenile Detention facility for investigation of first-degree murder, Denver television station KDVR reports.
Kiaya's father told police she disappeared on Wednesday last week after she went for a walk with his girlfriend's son to a nearby shopping centre in their home town in Illinois.
When the boy returned home without her, she was reported missing to police.
The boy told authorities the pair got seperated when it started raining.
Police haven't confirmed if the 15-year-old boy they have arrested is the father's girlfriend's son.
Kiaya's body was found the day after she was reported missing, about 1.6km from her house.
The coroner has not released the exact cause of death but confirmed it was "other than accidental," according to KDVR.
Police confirmed the death is being investigated as a homicide.
Kiaya was active on YouTube posting several videos over the past few years, sharing her life with the world.
Kiaya's mother has set up a GoFundMe page to help with final expenses.