ST. PAUL — The judge overseeing the federal trial of three former officers charged with violating George Floyd’s civil rights dismissed a juror Wednesday because his son is ill.

U.S. District Judge Paul Magnuson replaced the juror in the trial of J. Alexander Kueng, Thomas Lane and Tou Thao with an alternate.

Kueng, Lane and Thao are accused of depriving Floyd, 46, of his rights when they failed to give him medical aid as Officer Derek Chauvin knelt on the Black man’s neck for 9 1/2 minutes while Floyd was handcuffed, facedown. Kueng and Thao are also accused of failing to intervene in the May 2020 killing, which triggered protests worldwide and a reexamination of racism and policing.

Magnuson told the jury that a juror was excused because his son has a serious health condition.

Testimony began Jan. 24, after a jury was quickly selected days earlier. Twelve jurors will deliberate. Magnuson, concerned about COVID-19, ordered the selection of six alternates instead of the usual two in case any jurors became ill and had to drop out.

Prosecutors on Wednesday called Dr. Vik Bebarta, an emergency physician and toxicologist and professor at the University of Colorado in Denver, to testify. Bebarta said he concluded that Floyd “died from a lack of oxygen to his brain” and that he had suffocated because his airway had been closed off.

Bebarta’s testimony bolstered the prosecution’s contention that Floyd died because of how Chauvin pinned him down and the officers’ failure to roll him on his side, as they had been trained, so that he could have breathed easier. A lung specialist testified Monday that Floyd could have been saved if officers had moved him into a position to breathe more easily.

Bebarta said Floyd did not die from the low levels of fentanyl and methamphetamine in his system, nor from his heart disease and high blood pressure. He said that on video from inside a convenience store before his fatal encounter with police, Floyd did not appear to be seriously intoxicated or experiencing an overdose. But he did not dispute a store clerk’s earlier testimony that Floyd appeared to be high.

“He was awake, walking communicating, walking quickly at times,” Bebarta said.

Previous testimony has established that Chauvin — the most senior officer on the scene with 19 years of experience — told his fellow officers after Floyd became unresponsive, and they couldn’t find a pulse, to wait for an ambulance that was on its way. Officers kept restraining Floyd until the ambulance got there, according to testimony and video footage.

Kueng, who is Black, Lane, who is white, and Thao, who is Hmong American, are charged with willfully depriving Floyd of his constitutional rights while acting under government authority. The charges allege that the officers’ actions resulted in Floyd’s death.

Chauvin, who is white, was convicted of murder and manslaughter in state court last year and was sentenced to 22 1/2 years. He pleaded guilty in December to a federal civil rights charge.

Lane, Kueng and Thao also face a separate state trial in June on charges alleging that they aided and abetted murder and manslaughter.