Updated 7:37 p.m. ET

The Hennepin County Medical Examiner released a new autopsy report Monday, ruling George Floyd's death was a homicide. The office said Floyd's heart and lungs stopped functioning "while being restrained" by law enforcement officers.

Floyd died due to "cardiopulmonary arrest complicating law enforcement subdual, restrain, and neck compression," according to the report.

Louisville, Ky., resident David McAtee was shot and killed during a police response to a curfew violation early Monday. Both police and National Guard members were on the scene and fired shots. The incident has led to the firing of the police chief.

President Trump threatened Monday to take military action in American cities if the violent demonstrations that have been taking place in recent days aren't stamped out.

"If a city or state refuses to take the actions that are necessary to defend the life and property of their residents, then I will deploy the United States military and quickly solve the problem for them," Trump said in a short statement in the Rose Garden at the White House.

The plaza between St. John's Church and Lafayette Park was full of people nonviolently protesting police brutality late Monday afternoon when U.S. Park Police and National Guard troops, with the use of tear gas, suddenly started pushing them away for no apparent reason.

Sports are part of the fabric of American society, and often they've provided a medium for athlete protest. In recent years, former San Francisco 49ers quarterback Colin Kaepernick was the face of the movement. In 2016, he began kneeling before games, during the playing of the national anthem, to protest police treatment of minorities and social inequality.