(NEW YORK) -- A second fired police officer charged with violating George Floyd's civil rights during his 2020 fatal arrest testified on Wednesday and for the first time publicly explained why he helped his then-senior officer Derek Chauvin hold the handcuffed Black man to the pavement even after he was unable to detect a pulse.
J. Alexander Kueng, 28, took the witness stand in the high-profile federal trial after his co-defendant, Tou Thao, testified it was necessary to keep Floyd pinned to the ground, despite him being unconscious because he could "come back and fight again.”
"To save his life, we needed to hold him down for medical personnel," Thao testified on Wednesday.
Assistant U.S. Attorney LeeAnne Bell peppered Thao with questions on why he never attempted to get Chauvin, Kueng and a third officer, Thomas Lane, off of Floyd or step in to provide Floyd with life-saving medical assistance.
"I would trust a 19-year veteran to figure it out," Thao testified, referring to Chauvin, who was convicted last year in state court of murdering Floyd and sentenced to 22 1/2 years in prison.
Kueng began his testimony telling the jury that he grew up in North Minneapolis as the "soccer-obsessed" son of a Black father and a white mother.
He said he decided to go into law enforcement because he was "rubbed the wrong way" by Minneapolis police officers being "very rude and unhelpful" to people.
"If I wanted to see officers that citizens deserve, I should step up and be that person," Kueng testified
Under questioning from his attorney, Thomas Plunkett, Kueng said he joined the Minneapolis Police Department when he was 26 years old and was fast-tracked to get through the police academy.
Kueng said he learned early on that a field training officer was a "mentor, role model, educator and terminator."
He said Chauvin was "very quiet" and "by the book" as a field training officer. He said Chauvin was "fair but tough" and garnered "a lot of respect" from other officers who deferred to him on what to do at crime scenes.
Kueng testified that he and Lane, who was also a rookie, were the first officers to respond to a complaint that Floyd attempted to use a phony $20 bill at a Cup Foods store in south Minneapolis on May 25, 2020.
He said he didn't realize there was a potential problem until they approached a Mercedes-Benz SUV parked across the street from the store and he heard Lane yelling at Floyd, who was sitting in the driver's seat, to show him his hands. He said that as Lane ordered Floyd out of the vehicle, he noticed that Floyd seemed to have trouble walking and answering questions.
"He had some erratic behaviors," Kueng said of Floyd.
He said he noticed what appeared to be foam around Floyd's mouth that he noted was consistent with drug use.
Kueng testified that when he and Lane attempted to place the handcuffed Floyd in the back of their police vehicle, Floyd began to struggle and smashed his face against a Plexiglas partition separating the front seat from the rear seat.
"I've dealt with many strong individuals but I've never been involved in a struggle like I did with Mr. Floyd. It felt like I had no control," Kueng testified.
He said that when Chauvin and Thao arrived at the scene, they decided to remove Floyd from the police vehicle and place him prone on the street.
When Plunkett asked who was in charge of the scene, Kueng answered, "Officer Chauvin, sir."
"He was my senior officer and I trusted his advice," Kueng said.
Surveillance and body-camera video played at the trial showed Chauvin placing a knee on the back of Floyd's neck, while Kueng held down the man's midsection using his knee and Lane held down his legs.
Kueng said Floyd was thrashing around so forcefully that he had to reach out and grab hold of the squad car to avoid being bucked off of Floyd.
He acknowledged seeing Chauvin's knee on the back of Floyd's neck and upper back but said that based on his training, he didn't think that was unusual.
Video of the incident showed Floyd repeatedly complaining that he could not breathe, but Kueng said he was trained that if someone can talk they can breathe.
During the Kueng's testimony, Plunkett played a portion of police body-camera video in which Lane is heard asking whether they should get Floyd's legs up or turn him on his side to help his breathing. Chauvin responded, "just leave him" and Kueng repeated, "leave him, yep."
When Plunkett asked why he said that to Lane, Kueng said he was just passing down the message from Chauvin.
Plunkett asked Kueng about checking for a pulse after Floyd went quiet and appeared to lose consciousness. He said he checked Floyd's wrist because that was the only place available to check at the time and that he told Chauvin he couldn't detect a pulse, but assumed the handcuffs were causing Floyd to have a weak pulse.
Kueng said that he could not see the bystander witnesses on the other side of the squad vehicle, but when he saw Chauvin pull out his pepper spray canister, he assumed there was a threat and that the scene was not safe for them to render medical aide.
Kueng said he assumed Floyd was still breathing when paramedics took him away in an ambulance.
Plunkett asked Kueng when he realized Floyd was in serious medical need. Kueng answered that it wasn't until Lane came back to the scene after helping to load Floyd into the ambulance and assisting paramedics with CPR.
"It was a very very unstable situation that I don’t think was captured all that accurately on the body cam," Kueng said.
A prosecutor began the cross-examination of Kueng before court ended Wednesday by asking whether the Minneapolis Police Department's motto to "protect with courage and serve with compassion" matched his desire to become a police officer.
"Yes, ma'am," Kueng answered.
Kueng, Thao and Lane, who is also expected to testify, are charged with using the "color of the law," or their positions as police officers, to deprive Floyd of his civil rights by allegedly showing deliberate indifference to his medical needs as Chauvin kneeled on the back of the handcuffed man's neck for nine minutes and 29 seconds, ultimately killing him.
Kueng and Thao both face an additional charge alleging they knew Chauvin was kneeling on Floyd's neck but did nothing to stop him. Lane, who appeared to express concern for Floyd's well-being during the encounter, does not face the additional charge.
They have all pleaded not guilty.
ABC News' Whitney Lloyd contributed to this report.