The US Justice Department says it will not bring charges against two white police officers involved in the 2014 fatal shooting of a 12-year-old black boy who was holding a toy gun.
It said it was closing its investigation into the death of Tamir Rice in Cleveland, Ohio.
The shooting was one of several high-profile cases that gave rise to the Black Lives Matter movement.
In a statement on Tuesday, the justice department said that prosecutors had “found insufficient evidence to support federal criminal charges”.
Closing the case, it said it was not possible to prove beyond a reasonable doubt that either officer had wilfully broken the law, as opposed to making a mistake or exercising poor judgment.
“Although Tamir Rice’s death is tragic… both the Civil Rights Division and the US Attorney’s Office concluded that this matter is not a prosecutable violation of the federal statutes,” the department added.
The two officers, Timothy Loehmann and Frank Garmback, had been responding to an emergency call of a male brandishing a gun near a recreation centre.
However, the dispatchers failed to pass on the caller’s information that the person was a juvenile and that the “gun” might be a toy.
“The officers believed they were responding to a playground where a grown man was brandishing a real gun at individuals, presumably children,” the justice department’s six-page statement said.
Security camera video of the incident was found to be too grainy to show detailed circumstances of the shooting, the statement said.
The officers claimed that they told Rice to drop the weapon – but instead of dropping it he pointed it at them.
Police confirmed that the gun was a toy after Rice had been shot dead.
Although no charges have been brought over the case, in 2016 the city of Cleveland agreed to pay $6m (£4.4m) to Rice’s family.
Following Tuesday’s announcement, the family’s legal team said Rice’s mother was profoundly upset by the decision.
“Justice for the family would be to prosecute the officers who killed their child,” lawyer Subodh Chandra said.