The trial of Derek Chauvin, the ex-Minneapolis police officer charged in George Floyd’s death, resumes Tuesday with further testimony from an MMA fighter who witnessed Floyd’s arrest.

Donald Williams, 33, a wrestler and mixed martial artist who said he has worked with athletes and off-duty Minneapolis police officers, came upon Floyd’s arrest while walking to the Cup Foods convenience store on May 25, 2020.

Williams will continue his testimony – which could provide crucial insight into the potential cause of death – as both sides argue whether Floyd was killed by the officer through mechanical asphyxia or due to a heart arrhythmia exacerbated by methamphetamine and fentanyl in his system prior to the arrest.

As he first testified Monday, Williams described various chokeholds and how they are used. He described Chauvin’s position with his knee on Floyd’s neck as a “blood choke.” As he arrived outside the store, Williams said he noticed two police vehicles and a commotion.

“I noticed there were two police squad cars there … thought something’s going on, should I go back to my car or not?” Williams said on the stand. He then described how he heard Floyd in distress, saying, “My stomach hurts I can’t breathe, my head hurts, I can’t breathe … he pleaded with them.”

“I felt the officer on top was shimmying to actually get the final choke in while he was on top. Sometimes you could get in a blood choke and not know you’re in a blood choke until you’re unconscious,” Williams said, referring to Chauvin, who had his knee pressed to Floyd’s neck. Drawing from his training at the Minnesota Martial Arts Academy, Williams said he observed three factors about the restraint: the position of where the knee was on the neck, what body movements were happening while the knee was on the neck, and what was the condition of Floyd “while he was going through this torture.”

“One was that the neck was diagonal across the throat, which on a blood choke you tack the side of the neck,” Williams said. “You want to tack the side of the neck, cut the circulation of the breathing from your person, and then to get the choke tighter, you hit different shimmies, which I felt the officer on top was shimming, to actually get the final choking while he was on top to get the kill choke.”

Williams said he asked to check Floyd’s pulse and was “pissed off” with how another officer, Tou Thao, described Floyd’s reaction to the restraint, claiming the officer told the onlookers he was keeping back, “This is what drugs do to you.”

“Just like in MMA you could tell when someone get tired or you can tell when someone getting choked out or things like that…,” Williams said, describing how Floyd’s “breathing was getting tremendously heavy, tremendously harder for him to breathe.”

“And you actually can hear him,” he continued. “You could see him struggling to actually gasp for air while he was trying to breathe and he barely could move while he was trying to get there.”

In his opening statement Monday, Chauvin’s defense attorney Eric Nelson told jurors that the medical examiner in Hennepin County originally declared that this was a medical event – not as a result of the compression on the neck. Nelson went further to argue there was no evidence or contusion or injury in the neck area or windpipe and had nothing to do with asphyxia.

He claimed the government was displeased with that conclusion and sought outside experts typically not used in order to rebuff the conclusion of their own county medical examiner.

The Hennepin County Medical Examiner determined that Floyd’s cause of death was “cardiopulmonary arrest complicating law enforcement subdual, restraint and neck compression.” The manner of death was listed as “homicide.” Other significant conditions listed were “Arteriosclerotic and hypertensive heart disease; fentanyl intoxication; recent methamphetamine use.”

Floyd’s family later hired private doctors to conduct an independent autopsy, which listed the cause of death as “mechanical asphyxia” and the manner of death as “homicide.”