Protesters chanted "I can't breathe" in Boston's Dorchester neighborhood Thursday evening to condemn the killing of George Floyd in Minneapolis.
Four police officers have now been fired after Floyd, a black man, died in their custody.
In video of the incident, one of the officers has his knee on Floyd's neck.
"It's horrifying, but that type of thing happens even when the camera is off," said protester Kaj Berryman.
There have been protests across the country in response. Some have turned violent, but the one near the Ashmont MBTA stop in Boston was peaceful.
"We've got to look at our justice system and say 'no more,' that black people are respected, that their lives aren't taken away — they are not murdered by armed officers that are going rogue," said Rev. Joseph Rocha, a Boston community advocate.
Boston Police Commissioner William Gross said the officers involved in Floyd's death should be held accountable.
"There is nowhere in any of our training manuals that leaning on someone's neck is a proper procedure to quell an arrestees behavior," said Gross.
"I'm deeply disturbed by the death of George Floyd and my heart breaks for his family, for Minneapolis, and Black Americans everywhere," Boston Mayor Marty Walsh tweeted. "As leaders we must reflect on and learn from this tragedy and the history behind it."
Organizers say another protest is scheduled Friday at 5 p.m. at Peter's Park in the South End.