Here's Wikipedia on the details of that killing:
The shooting of Tamir Rice, a 12-year-old boy (June 25, 2002 – November 23, 2014), occurred on November 22, 2014, in Cleveland, Ohio. Two police officers, 26-year-old Timothy Loehmann and 46-year-old Frank Garmback, responded after receiving a police dispatch call "of a male black sitting on a swing and pointing a gun at people" in a city park. A caller reported that a male was pointing "a pistol" at random people in the Cudell Recreation Center. At the beginning of the call and again in the middle he says of the pistol "it's probably fake." Toward the end of the two-minute call, the caller stated "he is probably a juvenile." However, this information was not relayed to Loehmann or Garmback on the initial dispatch. The officers reported that upon their arrival, Rice reached towards a gun in his waistband. Loehmann fired two shots before the zone car came to a halt and within two seconds of arriving on the scene, hitting Rice once in the torso. Neither officer administered any first aid to Rice after the shooting. He died on the following day.
Rice's gun was later found to be an Airsoft replica that lacked the orange safety feature marking it as a replica and not a true firearm. A surveillance video of the shooting was released by police four days later, on November 26. On June 3, the County Sheriff's Office released a statement in which they declared their investigation to be completed and that they had turned their findings over to the county prosecutor, who will review the report and decide whether to present evidence to a grand jury.In the aftermath of the shooting, it was reported that Loehmann, in his previous job as a policeman in Independence, Ohio, had been deemed an emotionally unstable recruit and unfit for duty