Tamir Rice was playing with a replica gun at the edge of a park when a police car pulled up and shot him seconds later.
An onlooker called 911 and said there was a man with a weapon but cautioned the dispatcher that it was “probably fake”.
That message was not conveyed to Officers Timothy Loehman, 26, and Frank Garmback, 46, who rushed to the Cudell Recreation Center thinking they were confronting an armed man.
Security camera footage shows their squad car driving over grass up to the gazebo where Tamir was standing and had been pointing the toy gun.
Officer Loehman, who joined the force in March, is seen opening fire the moment he leapt from passenger’s seat. Tamir doubles over after being shot in the stomach at almost point blank range.
The two officers linger for a moment with their weapons drawn before Officer Garmback approaches the body.
Police said that the officers had warned Tamir to drop the weapon three times and that he appeared to be reaching for the gun when Officer Loehman opened fire.
There is no sound on the video and the footage is not clear enough to make out if Tamir was reaching for the toy.
Police in Cleveland released the footage after Tamir Rice’s family requested it be made public.
A grand jury made up of Ohio citizens will decide whether there is probable cause to charge either officer with a crime, based on evidence presented by local prosecutors.
The incident has parallels to the killing of Michael Brown, the unarmed black teenager whose death in Ferguson, Missouri, in August sparked days of unrest.
A grand jury decided on Monday that the white police officer who killed Mr Brown should not face charges but supporters of his family claimed that prosecutors made no real effort to secure an indictment.
The grand jury decision led to widespread looting and arson on Monday night but by Tuesday the situation had quieted as thousands of police and soldiers surged onto the streets of Ferguson.