A police officer was "justified" in pinning George Floyd to the ground before his death, says a use-of-force expert called by the defence team.
Barry Brodd told the trial in Minnesota that Derek Chauvin - who denies murder - acted with "objective reasonableness" during the arrest last May.
Video of Mr Chauvin kneeling on the neck of Mr Floyd led to worldwide protests against racism and policing.
Tensions are running high over a recent police shooting of a black man.
That happened on Sunday in a Minnesota suburb only 10 miles (16 km) away from the court where Mr Chauvin's trial is taking place.
On Tuesday, the court heard testimony from witnesses called by Mr Chauvin's defence team.
What did the expert say?
Former police officer Mr Brodd told the court that "the imminent threat" posed by Floyd was a major factor in his detention.
"I felt that Derek Chauvin was justified and acting with objective reasonableness following Minneapolis police department policy and current standards of law enforcement in his interaction with George Floyd," he said.
"From a police officer's standpoint, you don't have to wait for it to happen. You just have to have a reasonable fear that somebody is going to strike you, stab you, shoot you."
Mr Brodd added: "It's easy to sit in an office and judge an officer's conduct. It's more of a challenge to put yourself in the officer's shoes, to try to make an evaluation through what they are feeling, what they're sensing, the fear they have, and then make a determination."
Defence lawyer Eric Nelson asked Mr Brodd: "Was this a deadly use of force?"
"No, it was not," Mr Brodd replied.
He said that the crowd surrounding George Floyd during his arrest "posed an unknown threat" and drew Mr Chauvin's attention away from Floyd.
Cross-examining Mr Brodd, the prosecution maintained that the dangers of positional asphyxia - not being able to breathe in a certain position - were well known.
"Would you agree that that's something commonly understood in law enforcement?" prosecutor Steve Schleicher asked.
"Yes," Mr Brodd replied, confirming it was not new information.
His testimony was an attempt by the defence to rebut a number of medical experts called by the prosecution who said Chauvin used excessive, deadly force.
What else happened?
The trial also heard from Peter Chang, a Minneapolis Park Police officer who responded to the scene of Floyd's arrest. The court was shown footage from his bodycam.
Mr Chang told the court the crowd of bystanders around Floyd was "very aggressive to the officers".
"Did that cause you any concern?" Mr Nelson asked him.
"Concern for the officers' safety, yes," Mr Chang replied.
Shawanda Hill, an acquaintance of George Floyd, was compelled by the defence to testify on Tuesday.
She was sitting in the back seat of the car when Floyd was approached by store employees who confronted him over an alleged counterfeit $20 bill.
She said Floyd had earlier been "happy, normal, talking, alert".
She said that he had offered to give her a ride, and that she received a phone call while sitting in the car with Floyd.
While she was on the phone, she said Floyd suddenly fell asleep just before the employees came out to confront him.
She said she woke him again as the police arrived.
She said that as soon as Floyd woke up, the first thing he saw was an officer's gun. Ms Hill said that he immediately grew distressed and started pleading with the officers not to kill him.
"Did he seem startled when the officer pulled a gun on him?" the prosecutor asks.
"Very," she said.
What was the prosecution's case?
Last week the court heard from several expert witnesses who testified that Mr Chauvin's use of force was excessive.
They were also steadfast in their belief that Mr Floyd died from being subdued and not from drug use or ill health.
The police chief who fired the officer after seeing the video of him kneeling on Mr Floyd's neck told the court his actions went against all police training.
There were also eyewitnesses who described their concerns for Mr Floyd as they watched the arrest taking place.
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