ST. PAUL, Minn. (WCCO) — A Minneapolis police trainer and a doctor who tried to resuscitate George Floyd took the stand Thursday in the federal trial of three former Minneapolis police officers.

Tou Thou, Thomas Lane, and J. Alexander Kueng are accused of violating Floyd’s civil rights on May 25, 2020, when they failed to stop Derek Chauvin from kneeling on his neck for nearly 10 minutes, even as Floyd pleaded for air and lost consciousness.

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Chauvin has already pleaded guilty to the federal charges. Last April, a jury found him guilty of murdering Floyd, a crime for which he is currently serving a 22 and-a-half-year sentence.

In St. Paul’s federal courthouse on Thursday, Dr. Bradford Wankhede Langenfeld testified that the delay in getting Floyd aid contributed to his death. Langenfeld, who tried to resuscitate Floyd for nearly 30 minutes before pronouncing him dead at Hennepin Healthcare, said he tried to get Floyd’s heart beating again, but despite state-of-the-art care, Floyd never recovered.

Langenfeld testified that had CPR been given to Floyd earlier, his life could have been saved. “There is a limited window of time when you can act, and that window is very critical,” he said.

The doctor added that, in his opinion, Floyd did not die from the drug overdose, even though an autopsy revealed Floyd had fentanyl, methamphetamine and marijuana in his system. Langenfeld said that he believes mechanical asphyxiation, or a loss of oxygen, was the main factor. He also said that Floyd might have been experiencing excited delirium, a controversial diagnosis that is taught to first responders.

The defense teams from the three former officers have embraced the excited delirium diagnosis, saying that the officers were fearful of Floyd, because excited delirium can include supposed “super-human strength.”

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A Minneapolis police officer also took the stand Thursday. Inspector Katie Blackwell, the former commander of training for the department, said that officers are taught that they have a duty to provide medical aide, a duty to intervene if they see a fellow officer commit wrongdoing, and that arrests should involve the least amount of force necessary.

Blackwell testified that the duty to intervene was in the department’s policy book in May of 2020.

While all three of the officers on trial are charged with failing to provide medical aid to Floyd, Tou and Kueng are also charged with “willfully failing to intervene” against Chauvin.

In opening statements earlier this week, Thomas Plunkett, Kueng’s attorney, said that the “duty to intervene” was little more that a word on a PowerPoint training session at the time of Floyd’s death.

WCCO reviewed the current Minneapolis Police Department policy manual, and the duty to intervene section was last updated 10 days ago.

The three defense teams are working to pin the blame for Floyd’s death solely on Chauvin, as he was the senior officer at the scene and “calling all the shots.”

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Blackwell is expected to return to the witness stand Friday, continuing to testify on the training the three former officers received on intervention and providing medical care.

Esme Murphy