Former Minneapolis Police officer Derek Chauvin was found guilty on all charges by a jury in Minnesota for the killing of George Floyd last year.
The jury's verdict comes less than one year after video showing Chauvin kneeling on the back of Floyd's neck for more than nine minutes sparked nationwide outrage and led to mass protests against police brutality throughout the United States.
Prosecutors repeatedly showed excerpts from the video and in closing arguments, the state's attorney urged jurors to "believe your eyes."
"This case is exactly what you thought when you saw it first, when you saw that video," prosecutor Steve Schleicher said.
"This wasn't policing, this was murder," he said. "Nine minutes and 29 seconds of shocking abuse of authority."
Prosecutions of police officers are notoriously difficult in the United States because they enjoy what is called "qualified immunity," said David Schultz, a law professor at the University of Minnesota and Hamline University.
"Generally you can't hold police officers criminally responsible unless you can show they didn't follow department procedure or protocol, that they didn't act the way a reasonable officer would," Schultz said.
Prosecutors called several police officers to testify that Chauvin's use of force against Floyd, who was being taken into custody for allegedly passing a counterfeit $20 bill, was excessive.
They included the Minneapolis police chief Medaria Arradondo, who said Chauvin's actions violated the department's training policies and its "values."
Floyd's cause of death was also a key element of the trial and prosecutors called medical experts to testify that he died of hypoxia, or a lack of oxygen, from Chauvin's knee on his neck and that illegal drugs were not a factor.
Defense attorney Eric Nelson told the jury they needed to look at Chauvin's actions "from the perspective of a reasonable police officer."
"He did not purposefully use unlawful force," Nelson said. "You have to take into account that officers are human beings capable of making mistakes."
Nelson put a retired police officer on the witness stand who testified that in his opinion Chauvin's use of force against Floyd was "justified."
Nelson also sought to persuade the jury that Floyd's death was caused by an enlarged heart, narrowed arteries and the drugs fentanyl and methamphetamine.
A retired forensic pathologist put on the stand by the defense said Floyd died of cardiac arrest brought on by heart disease and the drugs.
Chauvin decided not to testify in his own defense and invoked his constitutional Fifth Amendment right against self-incrimination.
With additional reporting from AFP