Nigerian-American activist Opal Tometi: 'Why I co-founded Black Lives Matter'

Nigerian-American activist Opal Tometi co-founded the Black Lives Matter movement in 2013, after the killing of teenager Travyon Martin. The 17-year-old was fatally shot in Florida by George Zimmerman, who was subsequently acquitted on charges of second-degree murder and manslaughter, prompting a national outcry.

Opal Tometi tells the BBC's Aaron Akinyemi how and why the movement gained traction and what she hopes the revival of BLM in 2020 will achieve.