A gun owner with dementia or Alzheimer's disease will not be prosecuted in the case of a 3-year-old boy who accidentally killed his toddler brother with a bullet to the head as their shocked mother looked on, authorities said.

Police reports about the death released Thursday show the shooting occurred after the boys and their mother went to the apartment of 78-year-old Allen Duncan Haley to get food from his refrigerator.

Haley helped the family when they were in need.

Prosecutors suggested in a previous statement that Haley's condition and the unannounced visit by the family played a role in their decision against filing charges.

"Mr. Haley, who does not have children living with him and does not provide home care for children, is a frail, 78-year-old man who acknowledged he has 'issues' with his memory," the statement said.

Investigators said the child's mother had tried to keep the boys near her in the apartment, but they went to a bedroom as she filled boxes with food.

Later, she discovered the boys had left the room again and went to a bedroom where she found the 3-year-old with a .40-caliber handgun.

Before she could say anything, the gun went off and struck the younger boy in the head. He was pronounced dead at a hospital.

Police said there were three unsecured handguns in the apartment.

The weapon in the shooting was believed to have been covered by a towel. Haley also had rifles and other handguns that were locked in a safe.

Police said the 3-year-old had no understanding about the shooting. An investigator wrote that he didn't believe the boy even knew what the word "gun" meant.

In the immediate aftermath of the shooting, the 3-year-old wouldn't speak about what happened.

The Associated Press is not identifying the boys because of their age.