Man cleaning gun accidentally shoots, kills best friend: Police "My brother was messing with a gun and it went off," the 911 caller said.

A man was cleaning a gun when he accidentally shot and killed his best friend, police in Oklahoma said.

The man, who was not named by police, had been "cleaning/clearing" the semi-automatic handgun inside a mobile home in Midwest City -- just outside of Oklahoma City -- on Sunday afternoon, witnesses said, according to the Midwest City Police Department.

The gun accidentally discharged, and the man's friend, 21-year-old Joshua Allen, who was playing video games at the time, was fatally struck once in the chest, witnesses said, according to police.

"I need an ambulance fast," the 911 caller said, according to police. "My brother was messing with a gun and it went off accidentally hitting his best friend."

The investigation is ongoing but "all evidence indicates the shooting was not intentional," Midwest City Police Chief Brandon Clabes said in a statement Monday.

Clabes called the shooting "an unfortunate, tragic event while mishandling a loaded firearm."

The case will be presented to the district attorney's office to review for possible charges, said police.