we got all four! reporter: the autopsy commissioned by floyd s family found it was a homicide, and that the other officers seen in this video restraining floyd may have contributed to his death. the weight of the other two police officers on his back, who not only prevented blood flow into his brain, but also air flow into his lungs. reporter: the official medical examiner s autopsy also found it was a homicide, but pointing to cardiopulmonary arrest that was complicated by law enforcement restraint and neck compression. but family experts say it wasn t his heart, it was the pressure applied by officers. the day started with floyd s son quincy visiting the site. how important is change? what do you want to see happen? we need change. this can t happen to anybody else. reporter: quincy kneeling and praying where his 46-year-old father took his last breaths. tonight, applauding the arrests. my father should not have been killed like this. we deserve justice.
attack complicated by law enforcement restraint and neck constriction. the state s attorney general now vowing to charge others responsible, yet warning convictions might be a challenge. but that doesn t mean that when we get to a courtroom that it s going to be some sort of easy slam dunk. history proves that it isn t. reporter: terrance then leading a rousing tribute to the crowd. what s his name? george floyd! what s his name? george floyd! reporter: before leaving, seeking out a white protester in order to show a powerful moment of unity. after two relatively peaceful days here, the governor announced they will begin scaling back the national guardsmen that were mobilized here starting today. david? alex, thank you. protests already under way in new york, pittsburgh, philadelphia, denver, and elsewhere in this country. here in new york city tonight, where tension has been growing in the overnight hours for several days, there is a curfew in place at 11:00 p.m., th