Police in Denver used pepper spray after protesters gathered to listen to a "peaceful" violin vigil in memory of Elijah McClain, who died after US officers put him in a chokehold last year.
His death prompted a handful of small demonstrations over the last 10 months, but his case attracted renewed attention amid a global outcry sparked by the death of George Floyd while in police custody in Minneapolis last month.
Videos on social media showed thousands of demonstrators gathered outside a Denver police building on Saturday. The musical tribute was organised by the Party for Socialism and Liberation as Mr McClain, who was 23 when he died, was known for playing music to abandoned pets in animal homes to cheer them up. As the event progressed police accused people of throwing bottles and announced that the protest was now an “illegal gathering", according to the Denver Post.