MINNEAPOLIS (NewsNation Now) — A Minneapolis firefighter who voiced frustration at being prevented from using her EMT training to help George Floyd will be back on the stand Wednesday in the trial of the fired police officer charged in Floyd's death.

NewsNation will provide live coverage of the trial online and the NewsNation Now app. It is set to resume at 9:30 a.m. CT.

Genevieve Hansen, one of several bystanders seen and heard shouting at Derek Chauvin as he pinned Floyd facedown outside a convenience store last May, cried Tuesday as she recounted how she was unable to come to Floyd's aid or tell police what to do, such as administering chest compressions.

“There was a man being killed,” said Hansen, who testified in her dress uniform and detailed her emergency medical technician training. “I would have been able to provide medical attention to the best of my abilities. And this human was denied that right.”

Hansen was among several onlookers to testify Tuesday to what they saw of Floyd's May 25 death. They described their increasing frustration, anger and despair as they begged Chauvin to take his knee off Floyd’s neck.

This image from a police body camera shows people gathering as former Minneapolis police officer Derek Chauvin was recorded pressing his knee on George Floyd's neck for several minutes as onlookers yelled at Chauvin to get off and Floyd saying that he couldn't breathe on May 25, 2020 in Minneapolis. From the moment a bystander filmed the incident, video shaped the public's understanding of Floyd's death. (Minneapolis Police Department via AP)

Lawyers for Chauvin, 45, say he followed his police training and is not guilty of the charges brought by the Minnesota attorney general's office of second-degree murder, third-degree murder or second-degree manslaughter.

The defense has argued that Floyd’s death was not caused by the officer but by a combination of illegal drug use, heart disease, high blood pressure and the adrenaline flowing through his body.

A professional mixed martial arts fighter, Donald Williams, testified Tuesday he called 911 after paramedics took Floyd away, “because I believed I witnessed a murder.”

In this image from video, witness Donald Williams wipes his eyes as he answers questions, as Hennepin County Judge Peter Cahill presides Tuesday, March 30, 2021, in the trial of former Minneapolis police officer Derek Chauvin at the Hennepin County Courthouse in Minneapolis, Minn. Chauvin is charged in the May 25, 2020 death of George Floyd. (Court TV via AP, Pool)

Prosecutor Matthew Frank played back Williams’ 911 call, on which he is heard identifying officer Derek Chauvin by his badge number and telling the dispatcher that Chauvin had been keeping his knee on Floyd’s neck despite warnings that Floyd’s life was in danger. She offers to switch him to a sergeant.

As he is being switched, Williams can he heard yelling at the officers, “Y’all is murderers, bro!”

Williams calls Chauvin a “bum” in the video, accuses the white police officer of “enjoying” his restraining of Floyd, a 46-year-old handcuffed Black man, and told jurors on Monday he believed that Chauvin was using his knee in a “blood choke” on Floyd, a wrestling move to knock an opponent unconscious.

Chauvin’s lawyers counted that Williams does not have knowledge of police maneuvers.

Darnella Frazier, the Minneapolis teenager, whose cellphone video of the arrest went viral, cried in court as she testified Tuesday.

Frazier, 18, was walking her younger cousin to buy some snacks at Cup Foods, where a worker had moments before accused Floyd of using a fake $20 bill, when she saw police arresting Floyd outside and pulled out her cellphone.

Frazier testified that she began recording the scene because “it wasn’t right, he was suffering, he was in pain.”

Minutes later, Frazier’s young cousin took her place in the witness stand, saying in a small voice she recognized Chauvin as the man she saw kneeling on Floyd.

“I was sad and kind of mad,” the girl said.

Another bystander, 18-year-old Alyssa Funari, testified tearfully that she also felt helpless to intervene when she saw Floyd struggling to breathe as Chauvin knelt on his neck and other officers pinned down his lower body.

“I felt like there wasn’t really anything I could do as a bystander,” Funari said, adding that she felt she was failing Floyd. “Technically I could’ve did something, but I couldn’t really do anything physically … because the highest power was there at the time,” she said, explaining that an officer held the crowd back.

Prosecutors played cellphone video recorded by Funari that showed bystanders becoming more frantic and agitated as they watched Floyd stop moving. The video, which had not been released before, also showed the woman who said she was a Minneapolis firefighter calmly walk up to Thao and offer to help, before he ordered her to get back on the curb.

Chauvin attorney Eric Nelson sought to use the same evidence to show that Chauvin and his fellow officers found themselves in an increasingly tense and distracting situation, with the growing crowd becoming more and more angry over Floyd’s treatment.

But witnesses also testified that no bystanders interfered with police. When Frazier was asked by a prosecutor whether she saw violence anywhere on the scene, she replied: “Yes, from the cops. From Chauvin, and from officer Thao.”

Fourteen jurors or alternates are hearing the case — eight of them white, six of them Black or multiracial, according to the court. Only 12 will deliberate; the judge has not said which two will be alternates.

The Associated Press and Reuters contributed to this report. All reporting by AP’s Steve Karnowski and Amy Forliti and Reuters’ Jonathan Allen.