MINNEAPOLIS — An officer who trained Derek Chauvin on techniques he could use to subdue suspects testified Tuesday that the neck restraint he used on George Floyd was not authorized because Floyd was already handcuffed and under control.

Lt. Johnny Mercil, who oversees the Minneapolis department’s training on use of force and other defensive tactics, said that at the time of Floyd’s death on May 25, officers were permitted to restrain suspects by applying pressure to the side of a person’s neck to gain compliance, but only if they were actively resisting and if other techniques had not worked.

Prosecutor Steve Schleicher showed Mercil a still taken from bystander video of Chauvin kneeling on Floyd’s neck and asked if Chauvin was performing “a MPD-trained neck restraint.”

“No, sir,” Mercil replied. He said that “knee-on-the-neck is something that might happen” as officers try to gain control of suspects but said the act should stop when a person is no longer actively resisting. He said a neck restraint was considered “active aggression” under MPD use-of-force policy and that officers had been specifically warned to be careful of the neck because of the danger of rendering someone unconscious.

“We tell officers to stay away from the neck when possible,” Mercil said.

But Eric Nelson, Chauvin’s defense attorney, sought to raise questions about the positioning of his client’s knee on Floyd’s body and how long it was there. He showed Mercil four still images taken from police body cameras worn by other officers at the scene that appeared to show Chauvin’s knee near Floyd’s shoulder area at times.

The images, which Nelson admitted were “a little hard to see,” suggested they were taken at different moments beginning at about five minutes after Floyd was placed on the ground until an ambulance arrived at the scene, according to timestamps.

Does this appear to be a neck restraint?” Nelson asked as he presented a photo that appeared to show Chauvin’s knee near Floyd’s shoulder blades.

“No, sir,” Mercil replied.

Mercil was one of three Minneapolis police officers called to the stand Tuesday as prosecutors continued to rebut defense claims that Chauvin was following training and policy when he knelt on Floyd’s neck for over nine minutes.

Several veteran officers, including the city’s police chief, have testified that Chauvin violated department policies when he used his knee to pin Floyd, face down and handcuffed, on a South Minneapolis street as Floyd cried out that he couldn’t breathe.

As they began day seven of testimony, prosecutors called several officers who had directly trained Chauvin and showed the jury images of department records showing that he had taken courses that should have led him to respond differently at the scene with Floyd.

According to testimony, in 2016 Chauvin took a 40-hour course on how to recognize people in crisis, including those suffering mental health or drug problems. The course taught officers how to de-escalate those situations.

Sgt. Ker Yang, who oversees the department’s crisis intervention training program, said officers are trained on an invention model that focuses on respect and trust, and that once it is “safe and feasible” they should begin to de-escalate.

“When we talk about fast-evolving situations, I know that they do exist, they do happen,” Yang testified. “But a lot of the time, we have the time to slow things down and reevaluate, reassess.”

But in a maneuver that Nelson has frequently deployed in his cross-examinations, he pressed the sergeant on the pressure that officers face at scenes, including from bystanders, and whether that figures into the department’s crisis intervention response. Nelson has argued that Chauvin faced a hostile crowd at 38th and Chicago, which influenced his decision to keep Floyd restrained on the ground.

“Are there situations in your own experience where you have had to use force on someone and other people observing the use of force don’t like what you’re doing?” Nelson asked Yang, who responded in the affirmative.

“Sometimes that the public doesn’t understand that police actions can look really bad?” Nelson continued. “But they still may be lawful even if they look bad, right?”

“Yes, sir,” Yang said.

Nelson also raised the subject with Officer Nicole Mackenzie, the department’s medical services coordinator who was called to testify about Chauvin’s medical training. Prosecutors have argued Chauvin and the other officers at the scene — J. Alexander Kueng, Thomas K. Lane and Tou Thao — should have started CPR when it became clear that Floyd didn’t have a pulse.

But Mackenzie said under questioning from Nelson that officers should make sure “your scene is safe before you are able to render aid” and that chaotic scenes can be distracting to those trying to offer medical assistance.

“If you’re trying to be heads down on a patient that you need to render aid to, it’s very difficult to focus on the patient while there’s other things around you,” Mackenzie testified. “If you don’t feel safe around you, if you don’t have enough resources, it’s very difficult to focus on the one in front of you.”

Still, Mackenzie helped to make an important point for the prosecution, testifying that MPD officers are not trained to equate a person’s ability to talk with them being able to breathe. Body-camera video captured Chauvin dismissing Floyd’s claims of being unable to breathe, telling him it takes “a lot of oxygen to say that.”

“There is a possibility that somebody could be in respiratory distress and still be able to verbalize it,” Mackenzie said, echoing other medical experts. “Just because they’re speaking doesn’t mean they’re breathing adequately.”

The prosecution also called Sgt. Jody Stiger, a use-of-force expert with the Los Angeles Police Department, who testified that the amount of force Chauvin used was “excessive.”

Stiger, an aide to the LAPD’s inspector general and an officer with the department since 1993, said it is not typical for an officer to use “any type of force” in response to an incident involving a counterfeit bill. Officers initially were called to Cup Foods, the market outside of which Floyd died, to investigate a report of someone passing a fake $20 bill.

After reviewing all of the police body-camera footage, bystander videos, training manuals, and department policies and procedures related to the case, Stiger said, he concluded that the officers “should’ve de-escalated the situation” but instead continued to use force against Floyd.

Stiger testified that he has conducted about 2,500 use-of-force reviews in his career and trained close to 3,000 officers in use-of-force tactics.

Stiger, the first of two use-of-force experts prosecutors plan to call in the case, testified that based on his viewing of body-camera video, the officers were justified in using force to place Floyd in a squad car because he was actively resisting. But he said Floyd “slowly ceased his resistance” when he was placed on the ground.

“And at that point, the officers — ex-officers, I should say — they should have slowed down or stopped their force as well,” Stiger testified.

His testimony was interrupted several times by defense objections, after which Hennepin County District Judge Peter A. Cahill sent the jury home early.

Stiger, a frequent expert witness at trials who said he was paid $10,000 to examine the Chauvin case, is expected to resume his testimony Wednesday.

Before testimony began Tuesday, the court heard arguments over the proposed testimony of Morries Lester Hall, who was a passenger in the car that Floyd was driving the day he was killed. Hall has sought to squash a subpoena in the case, giving notice that he intends to invoke his Fifth Amendment right against self-incrimination.

Hall, who has been seen on several videos of the moments leading up to Floyd’s death, has been listed as a possible witness by both the prosecution and the defense — though Chauvin’s attorney indicated in his opening statement that he will be a key witness in their case that Floyd’s drug use that day resulted in his death, not the pressure from the former officer’s knee.

Last week, Courteney Ross, Floyd’s girlfriend, testified about the couple’s addiction to opioids and said they had gotten pills from Hall in the past. Separately, a store clerk at Cup Foods testified that Hall had tried to pass a counterfeit bill just hours before the store called 911 to report Floyd had allegedly passed a fake $20 bill.

Nelson indicated he wanted to ask Hall about Floyd’s drug use on the day of his death, whether the men had attempted to use fake currency at Cup Foods and his observations of Floyd’s interactions with police. Nelson also said he wanted to question Hall about security video that shows him dumping the contents of a backpack taken from inside the car while police were restraining Floyd across the street, and why he allegedly gave a fake name to police at the scene and later fled the state.

Hall, who was arrested last month in a separate case and is being held at a Minneapolis jail, appeared in court via a video feed as his attorney, Adrienne Cousins, argued her client has “been provided no immunity” in the case and could be exposed to a potential third-degree murder charge and other felony counts if forced to testify.

“There’s an allegation here that Mr. Floyd ingested a controlled substance as police were removing him from the car,” Cousins said. “This leaves Mr. Hall potentially incriminating himself into a future prosecution for third-degree murder.”

Cahill agreed that most of Hall’s testimony could be incriminating but suggested there could be a “narrow” window in which he could be questioned about Floyd’s behavior at the scene. But prosecutors argued against the jury seeing Hall invoke his right not to testify, arguing it would compromise the trial.

“This questioning would not exist in a vacuum,” prosecutor Matthew Frank said. “I don’t know how we put on Mr. Hall to testify and ask him one question and then let him leave without having the ability to pursue, as we normally would in a trial, the credibility and the foundation for that testimony in light of all we know.”

Cahill said the court would revisit the issue in coming days.

Meryl Kornfield contributed to this report.