According to Sheriff's Office investigators, the incident occurred on August 18.
The Cache County Sheriff’s office was notified of the death by the Medical Examiner’s office on Wednesday.
Sheriff's officials said there was a delay in reporting the initial incident because the mother of the three-year-old girl transported the child to the Franklin County Medical Center in Idaho on Thursday and that the victim was later transported to Primary Children’s Medical Center in Salt Lake City.
A medical examiner later determined that the child's death was caused by a BB gun shot to the head.
The Cache County Sheriff’s Office said investigations found that the victim’s two brothers, ages 11 and 9, were pumping up their BB guns and shooting the girl in the head with the air from the BB Gun.
On the last shot, investigators said that the nine year old brother pumped air into the gun and shot the victim with what he thought was air, but a BB was in the gun and struck the 3-year-old in the left side of the head.
The victim was then taken to the hospital, and later died at Primary Children’s Medical Center that same day.
The Sheriff's Office said that the case is still under investigation and that more interviews will be performed before the case is reviewed by the Cache County Attorney’s Office.
----Information from: Cache County Sheriff's Office.