Expert Witness in Derek Chauvin Trial Says His ‘Force Was Excessive’

While the first week of the trial brought emotional testimony from bystanders, Tuesday’s proceedings seemed to cement the trial into the second phase: focusing on whether Mr. Chauvin, who is accused of murder in Mr. Floyd’s death, violated police policy, or whether his actions lined up with his training. Here are the highlights from Tuesday.

• Mr. Nelson found some testimony from prosecution witnesses that could support his arguments. Officer Nicole Mackenzie, the medical support coordinator for the Minneapolis Police Department, agreed with Mr. Nelson’s assertion that a crowd of vocal bystanders can make it difficult for an officer to render medical aid during an arrest. Lt. Johnny Mercil, a veteran of the Minneapolis Police Department and use-of-force instructor, also said that hostile bystanders could raise alarm with officers. Mr. Nelson has suggested throughout the trial that the crowd outside the Cup Foods convenience store, which yelled at Mr. Chauvin as he knelt on Mr. Floyd for nine and a half minutes, might have hindered the former officer from helping Mr. Floyd once he became unresponsive.

• Mr. Nelson hit on a similar theme during the questioning of Sgt. Ker Yang, a crisis intervention coordinator with the Minneapolis Police Department. He asked whether an officer can “look bad” even when applying force that is lawful, and asked whether officers are tasked with weighing possible threats, such as a crowd of bystanders, when applying force. “You’re taking in a lot of information and processing it all kind of simultaneously through this critical decision-making model,” Mr. Nelson said. Sergeant Yang agreed.

• Los Angeles Police Sgt. Jody Stiger, a use-of-force expert, told prosecutors that Mr. Floyd kicked at officers as a possible attempt to break free from their grasp. Still, Sergeant Stiger said that kick was the only such attempt by Mr. Floyd. He also said that, based on his review of body camera footage, Mr. Floyd seemed to comply with officers shortly after they placed him facedown on the pavement, with his hands cuffed behind his back.

• When reviewing a picture of Mr. Chauvin pinning George Floyd to the ground, Lieutenant Mercil told prosecutors that Mr. Chauvin’s position was not consistent with the Minneapolis Police Department’s training on use of force. In addition, Lieutenant Mercil said that officers are trained to “use the lowest level of force possible” when controlling a subject. Mr. Chauvin kept Mr. Floyd pinned for several minutes even after he became unresponsive. Still, Mr. Nelson made some potential headway with the testimony of Lieutenant Mercil. Asked about neck restraints, Lieutenant Mercil said it generally takes less than 10 seconds for a person to become unconscious because of a neck restraint. The question could allow Mr. Nelson to argue that Mr. Chauvin’s knee did not qualify as a neck restraint, because it took several minutes for Mr. Floyd to lose consciousness.

Mr. Chauvin, the former Minneapolis police officer accused of killing George Floyd last year, faces charges of manslaughter, second-degree murder and third-degree murder.

On Thursday, roughly 3.7 million viewers were watching trial coverage on the three channels during the afternoon testimony of former Sgt. David Pleoger, who supervised Mr. Chauvin and testified that he should have “ended” his restraint after Mr. Floyd became unresponsive. That audience was larger than the number of people tuning into any other cable program that day. “The Rachel Maddow Show,” the most watched cable show on Thursday, drew three million viewers.

On Monday, the trial continued to attract a large viewing audience. CNN’s 3 p.m. hour, which featured testimony from Medaria Arradondo, the Minneapolis police chief, averaged 1.4 million viewers, the network’s highest total for the day, including its prime-time hours. HLN had an average of 470,000 viewers between 3 and 4 p.m. on Monday, also its most-viewed hour of the day.

The Nielsen figures do not reflect people who watched the trial on separate streaming outlets or on digital devices. Court TV is also broadcasting and streaming live trial coverage in its entirety. Fox News, the most-watched cable news network, has not been carrying the trial live.

HLN, a channel formerly known as CNN2 and CNN Headline News that is owned by CNN’s parent company, AT&T’s WarnerMedia, had its highest daytime ratings since 2013, when it covered the trial of George Zimmerman, a neighborhood watch volunteer who fatally shot Trayvon Martin, an unarmed Black teenager, according to Nielsen. HLN’s audience figures only continued to spike as the week went on.

“The numbers show that there is a high level of interest,” said Ken Jautz, an executive vice president of CNN, who oversees HLN, in an interview.

“This trial raises so many prominent and searing societal issues,” he continued. “Issues of policing practices, and how law enforcement treats people of color.”

On MSNBC, viewership figures for the morning portion of the trial went up throughout its first week. On March 29, 929,000 viewers watched the trial as it began just after 10:30 Eastern time. By Friday, the fifth day, MSNBC viewership figures for the morning portion had risen to 1.2 million viewers, according to Nielsen.

The figures are nothing close to interest to the 1995 O.J. Simpson trial. Roughly 50 million people watched the trial’s conclusion from their homes, a figure that may have been three times that size if the number of people watching it at work, at school or in airports or restaurants had been factored in.

The Chauvin trial is expected to last several weeks, and the three cable news networks are likely to continue broadcasting significant portions of it.

The lawyer, Eric J. Nelson, has repeatedly sought to argue that the group of people who yelled at police officers as they saw Mr. Chauvin kneeling on George Floyd may have forced his attention away from Mr. Floyd’s worsening condition.

Officer Mackenzie said it could be “incredibly difficult” to provide medical treatment in front of a loud crowd, even if they were not interfering physically.

“If you had a very hostile or volatile crowd — it sounds unreasonable — but bystanders do occasionally attack E.M.S. crews,” she testified.

Prosecutors have argued that the people who witnessed Mr. Floyd’s arrest presented no threat to the officers and were simply distraught over what they saw. They called Officer Mackenzie to the stand to bolster their argument that Mr. Chauvin, who was fired from the department and is facing charges including murder, violated police policies that required him to administer care to people in his custody when it was safe to do so.

But when Mr. Nelson asked if the police policies that require officers to administer care are “contingent upon what’s going on at the scene at the time,” Officer Mackenzie agreed.

She also described what she said were the effects of “excited delirium,” a controversial diagnosis that is often ascribed to people who die in police custody. Officer Mackenzie said that people experiencing excited delirium could exhibit “superhuman strength” because they do not feel normal levels of pain.

Mr. Nelson also showed images from a training slide show that she delivered to officers on the use of naloxone, the overdose-reversing treatment often known by the brand name Narcan. In that training, Officer Mackenzie noted that only a small amount of fentanyl can have deadly effects.

Fentanyl and methamphetamine were found in Mr. Floyd’s system, and Mr. Nelson has argued that the drugs may have caused his death.

There were parts of Officer Mackenzie’s testimony that helped the prosecution.

As police officers were arresting Mr. Floyd in May, and he was telling them he couldn’t breathe, one officer said it takes “a lot of oxygen” to talk. But Officer Mackenzie testified that someone who is having trouble breathing could still be able to speak, and that officers should not assume someone can breathe because they are talking.

“Just because they’re speaking doesn’t mean they’re breathing adequately,” she said.

At the end of the officer’s testimony, Judge Peter A. Cahill told her that Mr. Nelson was planning to bring her back to testify when he begins to lay out Mr. Chauvin’s defense.

Officer Mackenzie was the eighth current or former member of the Minneapolis Police Department whom prosecutors have called to testify. She said that when she was a rookie, Mr. Chauvin had filled in as her training officer for a day when her regular trainer was out sick. Mr. Chauvin had also attended training that she provided to the department.

And sometimes those field-training officers may be from an earlier generation that employed a more aggressive approach. That divide has been a concern of Minneapolis police and city officials as they try to change the way their officers operate after the death of George Floyd.

Mr. Chauvin, who is facing murder charges after kneeling on Mr. Floyd’s neck for more than nine minutes, was a field-training officer. He had supervised two of the rookie officers involved in Mr. Floyd’s arrest.

“Every police agency has a mission statement, but the culture is what is accepted by leadership on a day-to-day basis,” Sean Hendrickson, an instructor at Washington State’s police academy, told The New York Times in an article last year. “That gets backed up by other officers and is extremely deep and very difficult to change.”

Some activists have argued that the Minneapolis police — and other police agencies — were so irreparably broken that no amount of new training can reform them. Others have expressed concern that officers do not receive proper or enough training.

Most states require fewer minimum training hours to become licensed as a police officer than they do for barbers or cosmetologists. As of last year, for example, New York State law mandates 1,000 hours of training for massage therapists, compared with around 700 hours for officers. Hawaii has no minimum requirements for police officers, but manicurists must train for 300 hours.

Becoming a police officer in Minneapolis requires first getting a peace officer license from the state, which entails as many as 1,050 hours of training. Once recruits obtain their licenses, they have to go through additional training run by the Minneapolis Police Department that includes 19 weeks in the academy.

After completing the academy, new officers spend five months on the streets with a field training officer, who is supposed to teach recruits how to translate what they learned in the academy to real-life situations. But current and former officers pointed to one of the first things that field training officers often say to new recruits: “Forget everything you learned in the academy.”

Sergeant Stiger, a former Marine, joined the Los Angeles Police Department in 1993, according to a spokeswoman for the department. He holds the rank of sergeant II and serves as an aide to the office of the Inspector General, the body that oversees the police department and conducts performance audits, reviews use-of-force incidents and handles complaints of officer misconduct. He is the only sworn officer on staff.

He is also president of the Oscar Joel Bryant Foundation, which represents Black officers and civilian employees of the Los Angeles Police Department.

Sergeant Stiger served as a tactics instructor for in-service training for Los Angeles police officers for six years, during which he provided training regarding use-of-force policy and state law to about 3,000 officers, he said during his testimony.

He said he has conducted more than 2,500 reviews while working with the department and has consulted several entities on use-of-force reviews.

Sergeant Stiger was paid a flat fee of $10,000, as well as a trial fee, to review reports, video footage of the incident, training policies and other materials and ultimately make a judgment about whether the use of force by Mr. Chauvin was appropriate.

As he spoke, testimony continued inside the courtroom in the trial of Derek Chauvin, who has been charged with murder in George Floyd’s death. Ben Crump, a lawyer for the Floyd family, said the family had been told that autopsy photographs may be shown in court on Tuesday.

Prosecutors have already shown several graphic videos of the police confronting Mr. Floyd and Mr. Chauvin kneeling on him for more than nine minutes. Mr. Sharpton said he was praying for everyone watching the trial who was “suffering with” the Floyd family.

In addition to Mr. Crump and Mr. Sharpton, several high-profile Black politicians and activists accompanied the Floyd family. Among them were David A. Paterson, the former governor of New York; Gwen Carr, the mother of Eric Garner, who died in 2014 when a New York police officer put him in a chokehold; and Ray McGuire, who is running for mayor in New York and has secured Ms. Carr’s endorsement.

As two law enforcement officials in camouflage watched from a roof of the courthouse, several relatives of Mr. Floyd bowed their heads in prayer.

Afterward, Philonise Floyd, a brother of George’s, put his arm around Ms. Carr.

“We and Ms. Gwen Carr, after we get the verdict and we get this conviction, we’ll be able to breathe,” he said.

Steve Schleicher, a prosecutor, displayed a picture of Mr. Chauvin pinning George Floyd to the ground and asked, “Is this an M.P.D.-trained neck restraint?”

“No, sir,” Lieutenant Mercil responded.

The lieutenant, who is currently on medical leave from the Minneapolis Police Department, is the seventh member of the department to testify for the prosecution in Mr. Chauvin’s trial.

But Eric J. Nelson, a lawyer for Mr. Chauvin, countered with a line of questioning emphasizing the unpredictability of people who are being taken into custody, the possibility that they could stop resisting arrest and then suddenly become violent, and the challenge for police officers in assessing a situation as circumstances shift.

He suggested that Mr. Chauvin’s knee was not the cause of Mr. Floyd’s unconsciousness, and asked Lieutenant Mercil whether a restraint requires pressure on both sides of the neck for the person to go unconscious. “That is what we teach, yes,” he said.

Mr. Nelson repeatedly invoked the chaotic scene around Mr. Chauvin last May, asking Lieutenant Mercil whether bystanders yelling insults at an officer would “reasonably tend to rise alarm in an officer.” He agreed that they would.

Mr. Schleicher, the prosecutor, then asked: “And if they’re saying, ‘Get off him, you’re killing him,’ should the officer also take that into account and consider whether their actions need to be reassessed?”

“Potentially, sir, yes,” Lieutenant Mercil said.

A central question for jurors in this trial will be whether it was appropriate for Mr. Chauvin to kneel on Mr. Floyd’s neck for more than nine minutes. Johnny Mercil, a Minneapolis police lieutenant who provided use-of-force training to Mr. Chauvin, testified that officers were trained to “use the lowest level of force possible in order to meet those objectives.”

In many ways, this phase of the trial is putting police tactics on trial. Minneapolis residents, particularly African-Americans, have been highly critical of the Police Department, which they say has brutalized their communities. Since 2015, the Police Department has used force against Black residents at seven times the rate that it did against white residents, according to a New York Times analysis of police data last year.

About 20 percent of Minneapolis’s 430,000 residents are Black, but nearly 62 percent of the time that officers used force, it was against Black residents, according to the data.

Police officials argue that although the use of force may get a lot of attention, it is exceedingly rare. The data shows that there have been 4.3 million calls for service since 2008, but force was reported in just 13,472 of those instances, or just .31 percent of the time.

For residents who live in heavily policed areas, however, constant harassment by the police, even when force is not used, has left a bad impression. And shocking cases like Mr. Floyd’s can tend to overshadow the fact that force might be rarely used.

“When we talk about fast-evolving situations, I know that they do exist, they do happen,” Sergeant Yang testified. But in many situations, he added, “We have the time to slow things down and re-evaluate and reassess.”

His comments echoed those of Chief Medaria Arradondo, who on Monday testified that while Mr. Chauvin’s initial efforts to restrain Mr. Floyd may have been reasonable, he had violated policy by continuing to kneel on Mr. Floyd for more than nine minutes.

Mr. Schleicher noted on Tuesday that Mr. Chauvin had participated in a 40-hour crisis intervention training course in 2016.

Eric J. Nelson, Mr. Chauvin’s lawyer, pressed his argument that bystanders at the scene of an arrest can have a large effect on how an officer acts, and that an officer can “look bad” even while using force that is lawful. He also emphasized that officers are not supposed to remain solely focused on someone they are arresting, but are also supposed to consider other parts of their surroundings.

“It’s not just one small thing that you’re focused only on the subject that you’re arresting,” Mr. Nelson said. “You’re taking in a lot of information and processing it all kind of simultaneously through this critical decision-making model.” Sergeant Yang agreed.

Judge Peter A. Cahill, who is overseeing the trial of Mr. Chauvin, did not rule on whether Mr. Hall must testify, but he ordered Mr. Chauvin’s lawyer to draft a list of questions by Thursday that Mr. Hall might be able to answer without incriminating himself. Videos from the scene show that Mr. Hall was sitting in the passenger seat of a car when the police initially confronted Mr. Floyd, shortly before he was pinned to the ground and died.

Adrienne Cousins, Mr. Hall’s lawyer, said that both prosecutors and Mr. Chauvin’s lawyer, Eric J. Nelson, had subpoenaed Mr. Hall, though Mr. Nelson seemed more interested in calling him to the stand. Mr. Nelson said in court that he wanted to ask Mr. Hall a range of questions, including about whether he had given Mr. Floyd drugs, about the fake $20 bill that a convenience store clerk said Mr. Floyd used, and about why Mr. Hall left Minnesota after Mr. Floyd had died.

Ms. Cousins said that all of those questions could incriminate her client, and Judge Cahill largely seemed to agree. But the judge said there may be a narrow range of questions — possibly on how Mr. Floyd appeared to be acting in the car before the police arrived — that Mr. Hall might be able to answer without incriminating himself. Ms. Cousins strenuously disagreed, saying that even acknowledging that Mr. Hall was in the car with Mr. Floyd on May 25 could be used against him if he were to be charged with a crime based on his actions that day.

For their part, prosecutors seemed most worried about the prospect that Mr. Hall would take the stand and invoke his Fifth Amendment right in front of the jury, perhaps making them further question Mr. Floyd’s actions that day or making them concerned about what is being withheld.

Prosecutors should have started with “a more substantive argument early on, rather than an emotional one” because that is what the jurors are asked to consider in their decision, Mr. Hansford said. “We should be watching the expert testimony closely because that will be grounds” for the verdict, he said.

On Monday, the jurors heard none of the harrowing accounts of Mr. Floyd’s arrest. Instead, the prosecution guided the Minneapolis police chief, Medaria Arrodondo, through more than two hours of questions about the law, police training and standards. Prosecutors followed that with questions to the Police Department’s former training director about how often Mr. Chauvin would have received guidance on tactics such as restraining suspects, use of force and medical aid.

Chief Arrodondo testified that Mr. Chauvin violated the department’s policy when he pinned Mr. Floyd for more than nine minutes and failed to render aid.

On Monday, Chief Medaria Arradondo rebuked Mr. Chauvin — saying he pinned Mr. Floyd for too long and failed to render aid — in a rare example of a police chief testifying against a police officer. Though Mr. Chauvin’s restraints may have been justified at first, “Once Mr. Floyd had stopped resisting, and certainly once he was in distress and trying to verbalize that, that should have stopped,” the chief said.

Other witnesses included an emergency room doctor and veteran officer.

Dr. Bradford T. Wankhede Langenfeld, who attempted to save Mr. Floyd’s life at a hospital for about 30 minutes before declaring his death, said he believed that asphyxia, or the deprivation of oxygen, was one of the more likely causes of death. The prosecution has sought to validate that claim, while the defense has pointed to complications from drug use and a heart condition.

Inspector Katie Blackwell, a veteran police officer in Minneapolis, told jurors that officers should move suspects who are facedown and handcuffed “as soon as possible” because the position can make it difficult to breathe. Mr. Floyd was kept on his stomach even after he lost consciousness.

Mr. Chauvin’s lawyer, Eric J. Nelson, argued that officers sometimes have to juggle multiple things when applying force, such as possible threats from bystanders. Regarding Mr. Floyd’s cause of death, Mr. Nelson got Dr. Wankhede Langenfeld to confirm that drug use could cause asphyxia.

Ultimately, Monday’s testimony may prove problematic for the defense. The criticism by Chief Arradondo, in particular, could encourage the jury to break from the norm of giving police officers the benefit of the doubt when it comes to split-second decisions on when, and how, to apply force.

“He set a powerful example that police chiefs across the nation should follow when they know that their officers have violated people’s human rights and constitutional rights,” Ms. Armstrong said.

Residents and political leaders have been intensely debating the future of the city’s police department, with some activists and City Council members advocating the dismantling of the department and creating a new public safety agency that would oversee law enforcement. Some have said that the head of the new agency should not be a police officer, but Ms. Armstrong said that Chief Arradondo’s testimony instilled confidence in her that he should continue to lead law enforcement in Minneapolis.

“I think the fact that Chief Arradondo — not once, but twice — has been willing to break that blue wall of silence is incredibly important,” she said.

Other activists were not as impressed with the chief. D.A. Bullock is a local activist and filmmaker who said he favored defunding and dismantling the Police Department, and eventually abolishing it all together. He said he was disturbed that Chief Arradondo suggested that there were times when it was appropriate for officers to place their knees on the necks of suspects to get them under control.

That, Mr. Bullock said, “means to me that they are going to continue the practice of putting their knees on Black men’s necks.”

Like other supporters of efforts to defund the police, Mr. Bullock said he thought that Chief Arradondo was well intentioned. But he argued that the problems within the department were so systemic that there was little the police chief could do to make policing better.

“I encourage people again to look at the policy and not look at his performance,” Mr. Bullock said. “I don’t feel very confident in that testimony about actual changes in the Police Department.”

Minnesota has fairly clear and high standards for police officers, and unlike other states, it licenses and regulates its police officers, Mr. Schultz said. The defense will remind the jury that police officers across the country have statutory authorization to use force by way of a Supreme Court decision on qualified immunity, Mr. Schultz said.

“What Arradondo and the other police officers last week are doing is saying that Chauvin wasn’t a responsible police officer” based on the standards and training he had received, Mr. Schultz said. “This is what they have to do to show he engaged in criminal activity” and therefore lost his qualified immunity, he said.