An American grand jury has decided not to indict two white police officers over the fatal shooting last year of a 12-year old black boy as he played with a pellet gun. ______________________ 去年两名白人警察对玩玩具枪的12岁黑人男孩开枪射击导致其死亡.美国大陪审团决定不起诉两位白人警官.____________________