OFFICER Derek Chauvin had his knee on George Floyd’s neck and was bearing down with most of his weight the entire time Floyd lay face down with his hands cuffed behind his back, a use-of-force expert said at Chauvin’s murder trial.

Jody Stiger, a Los Angeles Police Department sergeant serving as a prosecution witness, said that based on his review of video evidence, Chauvin’s knee was on Floyd’s neck from the time officers put Floyd on the ground until paramedics arrived, more than 9 minutes, by prosecutors’ reckoning.

Prosecutor Steve Schleicher showed jurors a composite image of five photos taken from various videos of the arrest.

Stiger went through each photo, saying it appeared that the Minneapolis officer’s left knee was on Floyd’s neck or neck area in each one. He then confirmed that “particular force” did not change during the restrain period.

His evidence came a day after Chauvin’s lawyer, Eric Nelson, sought to point out moments in the footage when, he said, Chauvin’s knee did not appear to be on Floyd’s neck.

Nelson has also suggested that bystanders who were yelling at Chauvin to get off Floyd distracted the officers.

On Tuesday, the defence lawyer got police witnesses to acknowledge jeering onlookers can make it more difficult for officers to do their duty.

But Stiger told Schleicher: “I did not perceive them as being a threat”, even though some onlookers were name-calling and using foul language. He added that most of the yelling was due to “their concern for Mr Floyd”.

It was Stiger’s second day in the witness box. On Tuesday, he said officers were justified in using force while Floyd was resisting their efforts to put him in a squad car.

But once Floyd was on the ground and stopped resisting, officers “should have slowed down or stopped their force as well”.

Stiger said that after reviewing video of the arrest, “my opinion was that the force was excessive”.

Several experienced officers, including the police chief himself, have given evidence as part of an effort by prosecutors to dismantle the argument that Chauvin was doing what he was trained to do when he restrained Floyd last May.

Chauvin also took a 40-hour course in 2016 on how to recognise people in crisis, including those suffering mental problems or the effects of drug use, and how to use de-escalation techniques to calm them down.

Sergeant Ker Yang, the official in charge of the training, said officers are taught to “slow things down and re-evaluate and reassess”.

Records show Chauvin also underwent training in the use of force in 2018. Lieutenant Johnny Mercil, a police use-of-force trainer, gave evidence that those who attended were taught that the sanctity of life is a cornerstone of departmental policy and officers must use the least amount of force required to get a suspect to comply.

Under cross-examination by Nelson, Mercil said officers are trained in some situations to use their knee across a suspect’s back or shoulder and employ their body weight to maintain control. But Mercil added: “We tell officers to stay away from the neck when possible.”