Three additional Minneapolis police officers have been charged in connection with the May 25 death of George Floyd, which sparked protests against police violence across the country.

The officers are Tou Thao, Thomas Lane, and J. Alexander Kueng. Minnesota Attorney General Keith Ellison announced Wednesday that the officers have been charged with aiding and abetting second-degree murder.

Ellison also filed an upgraded charge against former Officer Derek Chauvin, who was arrested last week. Ellison filed a count of second-degree murder, in addition to the charge of third-degree murder filed last week.

“I believe the evidence available to us now supports the stronger charge of second-degree murder,” Ellison said.

Ellison also noted that prosecuting police officers can be difficult, but that the office filed the charges because it believes in them.

“George Floyd mattered,” he said. “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.”

The charges were first reported by the Star Tribune.

Floyd died after being pinned down by the neck for nearly nine minutes during an arrest.

Thao was seen on video watching as Chauvin held Floyd to the ground with his knee. Floyd was seen complaining that he could not breathe, and bystanders urged the officers to come to his aid, without avail.

The Hennepin County Medical Examiner’s office ruled the death a homicide, though it differed with an independent autopsy performed on behalf of the Floyd family in its conclusion on the precise cause of death. The family autopsy concluded that Floyd died of asphyxiation, while the coroner’s report indicated it was the result of the police restraint in combination with underlying medical conditions and intoxication.

All four officers were fired shortly after the arrest.

The Minnesota Attorney General’s office took over the case on Sunday, following a request from the Floyd family that the Hennepin County Attorney’s office be relieved of responsibility for the case. Some had complained that the local prosecutors office took too long to arrest and charge Chauvin, giving energy to the protests in Minneapolis.