Minnesota Attorney General Keith Ellison is increasing charges against former Minneapolis police officer Derek Chauvin to second-degree murder in George Floyd's killing and also charging the other three officers involved in the incident, according to a tweet from US Sen. Amy Klobuchar.

Ellison's official announcement is expected to come Wednesday afternoon, more than a week after Floyd was killed while in police custody in Minneapolis, sparking nationwide protests that call for the end to police violence against black citizens.

Derek Chauvin, who had his knee pressed into Floyd's neck for nearly nine minutes, had previously been charged with third-degree murder and second-degree manslaughter. Officers Thomas Lane and J.A. Keung, who helped restrain Floyd, and a fourth officer, Tou Thao, who stood near the others, were not initially charged.

Two autopsies on Floyd determined that he died by homicide. Minneapolis Police chief Medaria Arradondo fired the four officers and said they were "complicit" in Floyd's death, and Floyd's family and protesters nationwide have called for them to be arrested and convicted for the killing.

According to the video and the criminal complaint, Chauvin kept his knee on Floyd's neck as Floyd pleaded that he could not breathe, as witnesses protested that he was dying, and even as Lane twice asked to turn him onto his side. Still, Chauvin kept his knee on his neck for almost three minutes after Floyd became unresponsive, the complaint states.

Benjamin Crump, an attorney for the Floyd family, told CNN Wednesday that he is confident the other officers will be charged before Thursday's public memorial in Minneapolis.

"I am confident that these officers will be charged before people in Minneapolis say their final goodbyes to George Floyd, may he rest in peace," he said.