A large group of protesters chanted loudly as they marched down streets Friday night in downtown Memphis, voicing their frustration and solidarity days after the death of George Floyd, a handcuffed black man who died after a Minneapolis officer pressed his knee into his neck as he pleaded for air.

Floyd’s death, and the killings in past months of a black man in Georgia and a black woman in Kentucky, have led to violent protests in Minneapolis, Atlanta, Los Angeles, Phoenix and Columbus, Ohio, and peaceful demonstrations in other cities.

Four Minneapolis police officers were fired and investigations are underway after a white police officer was seen on video kneeling against the neck of Floyd.

Earlier Friday, Mayor Jim Strickland called for an investigation into whether an officer broke any rules after a video surfaced of a woman being knocked to the ground during a Wednesday protest related to Floyd’s death.

Strickland said on social media that he’s asked Police Director Michael Rallings to investigate “an event that occurred Wednesday night with one of our officers and a female protester.”