A white Chicago police officer has testified at his high-profile murder trial that he shot dead an African-American teen because he came too close and would not drop his knife. In the politically-charged case that has set America's third-largest city on edge, officer Jason Van Dyke shot Laquan McDonald 16 times in October, 2014. A police dash-cam video captured the incident.

The 17-year-old's killing has become emblematic of decades of police abuse in Chicago, and is one in a series of fatal encounters in recent years between US police and African Americans, who formed the Black Lives Matter Movement in response.