The first week in the trial of former Minneapolis police Officer Derek Chauvin, charged with the murder of George Floyd, concluded Friday with critical testimony from Lieutenant Richard Zimmerman, the longest serving officer in the Minneapolis Police Department. His testimony left no doubt that Chauvin’s use of force was unnecessary and led to Floyd’s death.

Zimmerman detailed the use of force training officers receive, noting police are trained to abide by the department’s use of force continuum. The policy, Zimmerman explained, involves officers continuously reevaluating and adjusting the level of force used against someone, depending on the “threat level” posed. After a person is in handcuffs, they represent no threat to officers, he said.

He also described the training he had received on the prone position, in which a person is placed face down on the ground. Zimmerman stated that a person should never remain prone, as Floyd was when officers pinned him to the pavement.

“Once a person is handcuffed, you need to get them out of the prone position as soon as possible because it restricts their breathing,” said Zimmerman. “If you’re laying on your chest, that’s constricting [breathing muscles] even more.”

After reviewing body cam footage of the incident, Zimmerman described the officers’ use of force as “totally unnecessary.” He stated he saw no reason why officers should have felt that they were in danger, adding that Floyd did not attempt to kick the officers, suggesting they had no reason to continue to use force while he was on the ground.

When asked about the crowd of bystanders, he testified that the crowd did not represent an “uncontrollable threat” that would have otherwise occupied officers’ attention. “It doesn’t matter—the crowd—as long as they’re not attacking you,” he said. “The crowd shouldn’t have an effect on your actions.”

The officers should have given Floyd immediate medical attention before paramedics arrived, Zimmerman said. Police are first responders and are given regular CPR training, and are, he noted, “absolutely” obligated to provide medical intervention to an injured suspect before an ambulance arrives.

The prosecutors have been building the case against Chauvin throughout the week. On Monday, Donald Williams testified that Chauvin knowingly used a “blood choke” on Floyd, cutting off blood flow to the brain, when he kneeled on Floyd’s neck for more than nine minutes. Williams said the only time Chauvin looked at him was when he called out that the officer was doing a “blood choke.” This moment was captured in the infamous image of Chauvin looking into the camera while on top of Floyd.

Darnella Frazier, a bystander who captured footage of the incident, broke into tears as she told the court she stayed awake some nights “apologizing and apologizing to George Floyd for not doing more and not physically interacting and not saving his life.”

A Minneapolis firefighter, Genevieve Hansen, testified Tuesday how she begged officers to check Floyd’s pulse when she arrived at the scene. Hansen explained that she was not on duty but immediately identified herself as a firefighter because she thought Floyd needed medical attention.

“There was a man being killed,” Hansen said. “I would have been able to provide medical attention to the best of my abilities, and this human was denied that right.”

On Wednesday, the court released new security and body camera footage played Wednesday showing accusations that Floyd was aggressive towards officers to be a complete lie. Officers drew a gun on Floyd within seconds of approaching him in his vehicle. Floyd begged officers not to shoot him and repeatedly said he did not know what was going on.

When officers tried forcing Floyd into the back of the police vehicle, he asked for officers to speak with him about the situation, telling them that he was scared and claustrophobic. Officers completely ignored Floyd’s clear signs of distress and escalated the situation.

Two EMS (Emergency Medical System) paramedics testified that Floyd was in a state of cardiac arrest when they arrived in an ambulance and that his heart never restarted.

Chauvin’s supervisory officer, retired Minneapolis Police Sergeant David Pleoger, told jurors that officers’ use of force against Floyd should have stopped as soon as he was handcuffed and on the ground. Pleoger denied the claim that the crowd was a more pressing concern than the care of Floyd.

Defense Attorney Eric Nelson argued that the evidence was beyond the more than nine minutes Chauvin kneeled on Floyd and sought to paint bystanders as an angry “distraction,” to suggest witnesses did not have the whole picture and to vilify Floyd’s character. Witnesses rebuffed these efforts, at times becoming confrontational, rightfully stating that seeing someone senselessly murdered was upsetting and were desperate to save Floyd’s life.

Testimony is set to resume Monday morning for further witness testimony and the presentation of evidence.