He also testified that handcuffed suspects can have difficulty breathing on their stomachs. He said officers are trained to move suspects into a side recovery position -- "the sooner the better."

However, Mercil said in cross-examination that Chauvin's position might be considered "using body weight to control," a tactic in which officers place a knee on a prone suspect's shoulder blades to handcuff them. He acknowledged that some screen grabs of police body-camera footage show Chauvin with his knee on Floyd's shoulders.

"However, I will add that we tell officers to stay away from the neck when possible, and if you're going to use body weight to pin, to put it on their shoulder and be mindful of position," he said.

Mercil said that the position is transitory and is meant to end once the suspect is under control.

In addition to Mercil, a crisis intervention training coordinator and a police CPR instructor each testified that officers are required to de-escalate situations and to render aid to those in distress.

Chauvin, 45, has pleaded not guilty to second-degree murder, third-degree murder and third-degree manslaughter. Defense attorney Eric Nelson has not indicated whether Chauvin will testify in his own defense.

Testimony in the trial began last Monday and was expected to last about a month.

Use-of-force expert says arrest was excessive

A Los Angeles Police Department sergeant hired by the prosecution as a use-of-force expert testified Tuesday that Chauvin and his fellow officers used excessive force in arresting Floyd last May.

LAPD Sgt. Jody Stiger, who said he has conducted over 2,500 use-of-force reviews, said officers were initially justified in using force when Floyd actively resisted arrest and refused to get into the squad car. Floyd also kicked at officers when he was first taken to the ground, body camera video shows. The circumstances then changed.

"However, once he was placed in a prone position on the ground, he slowly ceased resistance and at that point the ex-officers, they should have slowed down or stopped their force as well," Stiger said.

He said his opinion was based on the standard of what an "objectively reasonable" officer would do. The opinion took into account the low-level seriousness of Floyd's underlying crime -- allegedly using a $20 counterfeit bill -- as well as his actions, MPD policies and what officers knew at the time.

"They should have de-escalated the situation, or attempted to," Stiger said. Instead, "they continued the force that they were utilizing from the time that they first put him on the ground."

His testimony will continue on Wednesday.

Training coordinators explain officer requirements

The training coordinator for the Minneapolis Police Department's crisis intervention program testified Tuesday about the importance of recognizing when someone is in crisis and de-escalating the situation.

"Policy requires that when it's safe and feasible, we should de-escalate," said Sgt. Ker Yang, who has been with the department for 24 years.

Officers are trained in a critical decision-making model to address people in crisis that calls on them to continually assess and reassess what is needed in the situation, he said. Chauvin took a 40-hour course on crisis intervention training in 2016 in which actors portrayed people in crisis and officers had to de-escalate the situation, Yang testified.

In cross-examination, Yang said that the crisis intervention model can potentially apply to the suspect as well as nearby observers. The training advises officers to appear confident, stay calm, maintain space, speak slowly and softly and avoid staring or eye contact, he said.

Also on Tuesday, a Minneapolis Police medical support coordinator and CPR instructor testified that officers are required to render first aid and request emergency services when someone needs medical help.

"If it's a critical situation, you have to do both," Officer Nicole Mackenzie said.

The department teaches officers to determine the level of responsiveness for a person needing help. If the person is unresponsive, then the officer is required to check their airway, breathing and circulation, and if the person has no pulse, the officer should start CPR immediately.

She also said it's not accurate to say if someone can talk then they can breathe.

"That would be incomplete," Mackenzie said. "Just because they are speaking doesn't mean they are breathing adequately."

In cross-examination, she said that a hostile crowd could make it difficult to focus on a patient.

"If you don't feel safe around you, if you don't have enough resources, it's very difficult to focus on the one thing in front of you," she said.

"That in no way shape or form is anything that is by policy. It is not part of our training, and it is certainly not part of our ethics or our values," Arradondo said.

Passenger in Floyd's vehicle plans to plead Fifth

Morries Hall, who was in the car with Floyd when police first confronted them last May, appeared in court via Zoom on Tuesday prior to the jury arriving to discuss his intention to plead the Fifth if he is called to testify in the trial.

Both the prosecution and defense have called Hall as a witness. Nelson said he planned to ask Hall about his interactions with Floyd that day, their suspected use of a counterfeit bill, whether he gave Floyd drugs and his statements to police about Floyd's behavior in the vehicle.

Hall's attorney, Adrienne Cousins, argued that he planned to use the Fifth Amendment's right against self-incrimination, and she asked Judge Peter Cahill to quash his subpoena to testify. Cousins said she was concerned Hall's testimony could be used in a drug or third-degree murder charge against him.

"This leaves Mr. Hall potentially incriminating himself into a future prosecution for third-degree murder," Cousins told Cahill, noting the murder statute allows for prosecution of someone who provided drugs leading to an overdose.

Judge Cahill said that any questions about potential wrongdoing would not be allowed, yet he said he would be open to allowing specific questions about Floyd's behavior in the vehicle that day. He asked Nelson to draft specific questions on that point, which will be passed to Hall and his attorneys and discussed in a future hearing.

Hall's testimony could be key for the defense, who has argued that Floyd's cause of death was a mix of drug use and preexisting health issues.

Hall is currently in custody on unrelated charges of domestic abuse, domestic assault by strangulation and the violation of a protective order.