A follow-up to the OP. It looks like they put the suspected sergeant on administrative leave.
"Police and prosecutors in Boston are investigating after body camera footage showed officers pushing protesters, pepper-spraying crowds and one officer talking about hitting protesters with a police vehicle.
"A sergeant was placed on administrative leave after the leak of the footage captured during demonstrations in May after the killing of George Floyd by police in Minneapolis.
"The Boston protests on 31 May were mostly peaceful until night-time, when vandalism was reported. More than 50 people were arrested, 18 bystanders were hospitalized and nine officers were treated for injuries, Boston.com reported.
"The videos posted on Friday by the Appeal, an online news outlet, showed officers pushing nonviolent demonstrators to the ground, spraying pepper spray on people and into crowds, and one officer saying he may have hit people with a car."
https://www.theguardian.com/us-news/2020/dec/19/boston-police-officer-video-protesters-vehicle