CNN — A Minnesota judge found former Minneapolis police officer Tou Thao guilty of aiding and abetting second-degree manslaughter for his role in the May 2020 killing of George Floyd, according to court documents filed Monday.

In a 177-page verdict, Judge Peter Cahill wrote that Thao “actively encouraged his three colleagues’ dangerous prone restraint of Floyd” contrary to his training that the positioning could cause fatal asphyxia.

“Like the bystanders, Thao could see Floyd’s life slowly ebbing away as the restraint continued,” Cahill wrote in the verdict. “Yet Thao made a conscious decision to actively participate in Floyd’s death: he held back the concerned bystanders and even prevented an off-duty Minneapolis firefighter from rendering the medical aid Floyd so desperately needed.”

The decision marks the end of a series of state and federal trials for the four former officers involved in Floyd’s death, a killing captured on video that set off worldwide protests objecting to police violence against Black people.

“The conviction of Tou Thao is historic and the right outcome,” Minnesota Attorney General Keith Ellison, the lead prosecutor of Floyd’s murder, said in a statement. “It brings one more measure of accountability in the tragic death of George Floyd. Accountability is not justice, but it is a step on the road to justice.”

Derek Chauvin, Thomas Lane, J. Alexander Kueng and Thao were fired and arrested for their actions – or lack thereof – in May 2020 as Chauvin pressed his knee into the neck and back of Floyd, who was handcuffed and lying on his stomach, for more than nine minutes.

During the incident, Thao was standing nearby and ordered concerned residents not to interfere with police. Even as Floyd pleaded for air and for his mother, Thao made mocking references to Floyd’s assumed drug use and kept the group of bystanders from helping.

At his federal trial in 2022, Thao testified he assumed the other officers on the scene were “taking care” of Floyd, and that his role transitioned to crowd and traffic control. When prosecutors asked Thao during cross-examination why he didn’t tell Chauvin to get off Floyd’s neck, he said: “I think I would trust a 19-year veteran to figure it out.”

All of the former officers have been convicted of crimes in the years since then.

Lane, Kueng and Thao were found guilty in federal court of violating Floyd’s civil rights and of failing to intervene to stop Chauvin during the restraint. Thao is already serving a 3.5-year sentence for his February 2022 conviction on the federal charges.

In the state cases, Kueng and Lane pleaded guilty to aiding and abetting second-degree manslaughter and were sentenced to 3.5 years and 3 years in prison, respectively.

In October 2022, Thao agreed to a trial by stipulated evidence in the state case, waiving his right to a trial by jury and allowing his fate to be decided by Cahill after reviewing evidence presented by both parties.

Calls to Thao’s attorney and lawyers representing the Floyd family were not immediately returned Tuesday. Sentencing is set for August 7.