The trial for Derek Chauvin, the former Minneapolis police officer charged in the death of George Floyd, began Monday in Minneapolis.
He faces charges of manslaughter, second-degree murder and third-degree murder.
The trial is expected to last four weeks.
Donald Williams, the professional mixed martial arts fighter who can be heard in a witness video criticizing Minneapolis police officers during their encounter with Floyd, was called by the prosecution as its third witness Monday.
Williams was walking around the corner from the Cup Foods when he heard a commotion and saw Floyd on the ground with Chauvin kneeling over him, he testified.
Floyd "was speaking in a distressed way" when Williams got there, vocalizing to the officers that he was in pain and that he wanted his mom, Williams said.
"His breathing was getting tremendously heavy," Williams said, adding that it was apparent that he was struggling to gasp for air.
At one point, Floyd's eyes then "slowly rolled to the back of his head" and his nose started bleeding, and soon after he was "lifeless," Williams said.
Williams said his experience as a fighter led him to believe that Chauvin's position on Floyd's neck was putting Floyd in imminent danger.
Another witness on the scene who is a paramedic told the officers multiple times to check Floyd's pulse, but no one did, Williams said.
Alisha Oyler, a shift manager for the Speedway located across the street from Cup Foods, first noticed police officers “messing with someone” when she began watching the encounter involving Floyd, she told prosecutors Monday.
Oyler took seven separate video recordings on her cellphone but could not immediately recall details, stating that it had "been so long."
During a cross-examination, defense attorney Eric Nelson walked 911 dispatcher Jena Scurry through the timeline of the encounter and pressed her on her knowledge of Minneapolis Police use of force policies.
Nelson seemed to want the jury to know that Scurry was not familiar with how police handled such incidents.
Scurry acknowledged that she has only seen police incidents play out live on monitors in the dispatch center three to four times in the seven years she has been a dispatcher.
ABC News’ Whitney Lloyd contributed to this report.
