MINNEAPOLIS – Prosecutors charged a Minneapolis police officer accused of pressing his knee against George Floyd's neck with a new more serious charge of second-degree murder on Wednesday, and for the first time leveled charges against three other officers at the scene, according to criminal complaints.

The updated criminal complaint against Derek Chauvin says the officer’s actions were a “substantial causal factor” in Floyd’s death.

“Officer Chauvin’s restraint of Mr. Floyd in this manner for a prolonged period was a substantial causal factor in Mr. Floyd losing consciousness, constituting substantial bodily harm, and Mr. Floyd’s death as well,” the criminal complaint said.

The complaints against the other officers allege they aided and abetted in Chauvin’s actions. Minnesota Attorney General Keith Ellison said warrants have been issued for their arrests. Chauvin was already in custody.

Widely seen bystander video showing Floyd’s May 25 death has sparked protests nationwide and around the world against police brutality and discrimination. Chauvin was fired May 26 and initially charged with third-degree murder and second-degree manslaughter. The three other officers involved were also fired but were not immediately charged.

Ellison updated the complaint against Chauvin to add a charge of unintentional second-degree murder, in addition to the earlier charges. He also charged Thomas Lane, J. Kueng and Tou Thao with aiding and abetting second-degree murder and second-degree manslaughter.

The unintentional second-degree murder charge alleges that Chauvin caused Floyd’s death without intent while committing another felony offense, namely third-degree assault. It carries a maximum penalty of 40 years in prison, compared with a maximum of 25 years for third-degree murder.

The other officers face the same maximum penalties for aiding and abetting, if convicted.

“George Floyd mattered. He was loved, his family was important, his life had value, and we will seek justice for him and for you, and we will find it,” Ellison said.

Attorney Earl Gray, who represents Lane, told The Associated Press that he hadn’t seen the complaint or talked with his client. He said Lane was not in custody. Before news of the upgraded charges, an attorney for Chauvin said he was not making any statements at this time. Attorneys for Thao and Kueng did not return messages seeking comment on the charges.

Attorney Ben Crump tweeted that the Floyd family was “deeply gratified” by Ellison’s action and called it “a source of peace for George’s family in this difficult time.” He said Ellison had told the family his office will continue to investigate and upgrade charges against Chauvin to first-degree murder if warranted. Reached by phone, Crump declined to speak beyond the statement or make clear when Ellison had spoken with the family and whether he had been informed directly that additional charges had been filed.

Floyd’s family and protesters have repeatedly called for criminal charges against all four officers as well as more serious charges for Chauvin, who held his knee to Floyd’s neck, despite his protests that he couldn’t breathe, and stayed there even after Floyd stopped moving. Floyd, a black man, was in handcuffs when he died with his face pressed to the street.

“He died because he was starving for air,” Crump said at a news conference earlier Wednesday. “He needed a breath. So we are demanding justice. We expect all of the police officers to be arrested before we have the memorial here in Minneapolis, Minnesota, tomorrow.”

Crump said the other officers failed to protect a man who was pleading for help and said he couldn’t breathe.

Personnel records released by the city show Chauvin served as a military policeman in the U.S. Army in the late 1990s. Since being hired as a police officer in 2001, he has been awarded two medals of valor: One for being part of a group of officers who opened fire on a stabbing suspect after the man pointed a shotgun at them in 2006, and one for apprehending another man in a domestic incident in 2008. In the latter incident, Chauvin broke down a bathroom door and shot the man in the stomach.

Chauvin was reprimanded in 2008 for pulling a woman out of her car in 2007, frisking her and placing her in his squad car after he stopped her for speeding 10 miles per hour over the limit. His dashboard camera was not activated and a report said he could have interviewed the woman while standing outside her car.

Lane, 37, and Kueng both joined the department in February 2019 and neither have any complaints on their files.

Lane previously worked as a correctional officer at the Hennepin County juvenile jail and as a probation officer at a residential treatment facility for adolescent boys.

Kueng was a 2018 graduate of the University of Minnesota where he worked part-time on campus security. He also worked as a theft-prevention officer at Macy’s in downtown Minneapolis while he was in college.

Tou Thao, a native Hmong speaker, joined the police force as a part-time community service officer in 2008 and was promoted to police officer in 2009. He was laid off later that year due to budget cuts and rehired in 2012.

Gov. Tim Walz and the Minnesota Department of Human Rights on Tuesday launched a civil rights investigation of the Minneapolis Police Department and its history of racial discrimination, in hopes of forcing widespread change.