Former police officer Derek Chauvin, who is accused of murdering George Floyd, used inappropriate “deadly force” when kneeling on his neck for more than nine minutes, an  expert testified in his trial in Minneapolis on Wednesday.

Jody Stiger, a use-of-force specialist, was testifying for the prosecution in Chauvin’s trial.

Stiger, a Los Angeles police officer, said that Chauvin’s actions were “deadly force” because Floyd “was in the prone position.”

“And the pressure being caused by (Chauvin’s) body weight could cause positional asphyxia, which could cause death,” Stiger said, after being shown pictures of the scene.

Also read: Derek Chauvin Trial: Key witness avoids giving evidence

Asked how much force was reasonable when Floyd was lying on his front, handcuffed and not resisting, Stiger said “no force should have been used once he was in that position.”

“An officer is only allowed to use a level of force that is proportional to the seriousness of the crime, or the level of resistance,” he said.

Defense attorney Eric Nelson asked Stiger if use-of-force sometimes “looks bad, but it’s still lawful.”

Stiger agreed, saying “yes, based on that department’s policies or based on that state’s law.”

Prosecutors are seeking to prove that Floyd’s death was due to asphyxiation, while Chauvin’s defense claims it was due to illegal drugs in Floyd’s system.

Stiger said video footage suggested that the small crowd gathered at the site was not a hostile threat or a distraction for the officers — challenging one apparent defense strategy to explain Chauvin’s actions.

He also testified that Chauvin squeezed Floyd’s fingers and pulled his wrists using a technique to force people to comply to orders, but that Chauvin continued when Floyd offered no resistance.

And Stiger said police were trained to avoid the neck when handling people, and to always put them on their side or seated when handcuffed.

Also read: George Floyd trial: Police training instructor says ‘leg-neck restraints’ not trained in service

Another officer taking the stand Wednesday, James Reyerson, a lead investigator into the death, estimated that Chauvin weighed about 140 lbs (63 kilograms) and carried 30-40 lbs of equipment when he knelt on Floyd.

Chauvin has pleaded not guilty to charges of murder and manslaughter.

Floyd was arrested on suspicion of passing a counterfeit $20 bill in a nearby store.

The harrowing images of Floyd’s arrest in May 2020 touched off protests against racial injustice and police brutality in the United States and around the world.

Chauvin, who has been in court every day taking meticulous notes and consulting with his attorney, faces up to 40 years in prison if convicted of the most serious charge — second-degree murder.