Police at the scene of a shooting of a 12-year-old black boy at a playground in Cleveland, Ohio, believed he was about 20, according to recordings of the incident.
Tamir Rice was shot twice and later died in hospital.
Cleveland police have released video and audio recordings of the incident.
A CCTV video shows the boy pointing a toy gun at a passer-by at the playground, which prompted a 911 emergency call, the BBC reported.
Recordings of radio communications reveal that an officer after the shooting described Tamir Rice as aged "maybe 20".
A separate recording appears to confirm the officers were not told the gun might be fake.
Police said the family gave permission for the video recordings of the shooting to be released.
'Shots fired, male down'
The footage shows the boy walking around a playground with a replica gun clearly in his hand. Minutes later, a police car drives up and stops immediately next to him.
Chief officer Edward Tomba said that the car door was open when the officers arrived, and that they had ordered the 12-year-old to show his hands three times as the car pulled up, the BBC reported.
The boy was then shot and fatally wounded.
In a recording immediately after the incident, a police officer is heard saying: "Shots fired, male down, black male, maybe 20."
A recording of the call from the operator to police officers as they were dispatched to the scene appears to confirm that there was no mention of a replica gun.
The operator describes the incident as "a black male sitting on the swings, keeps pulling a gun out of his pants and pointing it at people".
An audio recording of the 911 emergency call had previously revealed that the caller had said the gun was "probably a fake" on two occasions, before adding he was not sure whether it was "real or not".