Police officers attend the funeral of slain New York Police Department officer Liu Wenjian in Brooklyn of New York City, the United States, Jan. 4, 2015. Liu and his parter Rafael Ramos were fatally shot in the head as they sat in their patrol car in Brooklyn on Dec. 20, 2014. The killer, Ismaaiyl Brinsley, who killed himself soon after, had said he was seeking to avenge white police officers' killing of two unarmed black men this summer. [Xinhua]