Updated April 6, 2021 at 1:00 PM ET

Lt. Johnny Mercil, who has been in charge of teaching the use of force in the Minneapolis Police Department's training division, says former officer Derek Chauvin's use of his knee on George Floyd's neck is not a technique the police teach when instructing officers how to restrain people.

Mercil is the latest in a string of police officials who are testifying about the department's training and Chauvin's use of force against Floyd, who died in police custody last May. Chauvin is facing murder charges in the death.

Displaying a photo of Chauvin holding his knee on Floyd's neck and looking up at a bystander, prosecutor Steven Schleicher asked Mercil, "Is this an MPD-trained neck restraint?" "No sir," Mercil replied.

He added that a "knee on the neck would be something that does happen in the use of force that is not unauthorized."

How long such a restraint is applied would depend on the level of resistance the subject is offering, Mercil said. When the prosecutor asked if the method would be authorized if someone is under control and handcuffed, he replied, "I would say no."

Mercil also said that in some cases, it might be appropriate to put a knee on someone during handcuffing – and to keep a knee there if the subject is still trying to thrash around or kick people. But he also said that people who are in handcuffs and are in the prone position should be moved either to the recovery position – on their side – or to a sitting or standing position, to avoid positional asphyxiation.

As for when a person who is no longer resisting should be moved from a prone position, Mercil said, "I would say sooner the better."

Describing the police use of neck restraints, Mercil said the department's training calls for officers to use their arms to restrict the flow of blood to and from the brain by applying force to the side of the neck "with the intent to gain control of a subject." He also said that while neck restraints can be performed with the legs rather than the arms, his unit doesn't teach officers to do that in their in-service training.

"As far as my knowledge [goes]," he added, "we never have."

Referring to moves often seen in mixed martial arts competitions, Mercil said that people who perform such a restraint commonly use their inner thigh and their opponent's arm to apply pressure.

Minneapolis police policy bars the use of neck restraints in any situation where a person is not "actively resisting," Mercil said. The policy also requires officers to keep the subject under "close observation" after applying a neck restraint.

During one part of his testimony, a courtroom display showed what Mercil said is commonly referred to as the "continuum of force," with officers' actions rising along with levels of a subject's resistance level.

Officers are told to de-escalate the level of force, the graphic showed, when they "can clearly defend or control with less force."

Another graphic taken from police training showed a map of the human body, with "red zones" marking areas where serious injuries were likely to occur, including the neck, head and chest.

Mercil, who is currently on medical leave, told the court he helped to develop and approve the department's curriculum that was used in 2018 – the year Chauvin took an in-service course on the use of force.

The "purpose and policy" section of the training lists three items, drawn from the police policy manual:

Mercil said he first became a use-of-force instructor in 2010. He started studying martial arts in college, including Brazilian jiujitsu. The methods he teaches, he said, range from using body leverage to "pain compliance."

Mercil also discussed proportionality and how that is taught to trainees.

"You want to use the least amount of force necessary to meet your objectives, to control" someone, Mercil told the jury. And if those lower uses of force don't work or are unsafe, he added, an officer can escalate the level of force.

Earlier Tuesday, jurors heard from Sgt. Ker Yang, the crisis intervention training coordinator for the Minneapolis Police Department.

Describing the Minneapolis police force's critical decision-making model, Yang said officers must assess situations and respond to evolving events. The model works in the field, he said.

Defense attorney Eric Nelson asked Yang about public perceptions of police activity and the possibility that onlookers can create or add to a crisis. Yang agreed that crowds can create a crisis in addition to what officers may already be dealing with.

Nelson also asked about potential signs of aggression, either in a subject or a bystander. Citing police guidelines, Yang said the signs include "standing tall, red in the face, raised voice, rapid breathing," along with muscle tension, pacing and other behaviors.

Yang agreed with Nelson that as the intensity of a person's crisis grows, the risk to officers and others also rises.

On the prosecution's follow-up questions, Schleicher asked how officers should differentiate between "big things" and "little things" in situations.

Assessing someone's medical condition for possible emergency aid "would be a big thing," Yang said.

When Schleicher asked how a 17-year-old filming an officers' actions would be classified, he replied, "The filming would be a small thing."

Chauvin, 45, is facing three criminal charges, as listed in court documents:

During Monday's court session, Inspector Katie Blackwell, who used to run the Minneapolis Police Department's police training unit, told jurors that Chauvin was not following the training he received when he held his knee on Floyd's neck for about nine minutes.

"I don't know what kind of improvised position that is," Blackwell said of the way Chauvin restrained Floyd. "That's not what we train."

Citing police policy, Blackwell said that "a neck restraint is compressing one or both sides of the neck, using an arm or a leg. But what we train is using one arm or two arms to do a neck restraint."

Blackwell now commands the 5th Precinct. She started testifying shortly after Minneapolis Police Chief Medaria Arradondo told jurors that Chauvin's actions ran against his department's values.

"There is an initial reasonableness in trying to get him under control in the first few seconds," Arradondo told the jury on Monday.

The chief continued: "But once there was no longer any resistance, and clearly when Mr. Floyd was no longer responsive and even motionless, to continue to apply that level of force to a person proned out, handcuffed behind their back – that in no way, shape or form is anything that is by policy, is not part of our training and is certainly not part of our ethics or our values."

Tuesday's court session began with a Zoom appearance by Morries Lester Hall, as NPR member station Minnesota Public Radio reported. Hall was with Floyd in his SUV and the Cup Foods store before the police were called last Memorial Day over an allegedly counterfeit $20 bill.

Hall has sought to avoid testifying in Chauvin's trial, with his attorney recently saying he would invoke his Fifth Amendment right against self-incrimination. Previous testimony in the case has depicted Hall as the man who first tried to pass an allegedly fake $20 bill to store clerks and also as a person who Floyd's girlfriend said had sold drugs to the couple.

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