Dr. Jonathan Rich, a cardiologist at Northwestern Memorial Hospital in Chicago, was the first on the stand in the third week of Chauvin’s murder trial.

During his testimony, Rich explained he was given access to a variety of information regarding Floyd’s death, and made an “expert report” using that insight.

“I was provided with a lot of evidence to look through, but mostly I looked at the medical records, interviews, all the videos that were provided to me, and the autopsy report,” Rich explained, adding that he also included several “journal articles” in his report.

Asked later if he had arrived at a conclusion with “a reasonable degree of medical certainty” as to the cause of Floyd’s death, Rich said he had.

“In this case, Mr. George Floyd died from a cardiopulmonary arrest,” Rich said Monday. “It was caused by low oxygen levels and those low oxygen levels were induced by the prone restraint and positional asphyxiation that he was subjected to.”

Rich also noted during his testimony that, after reviewing the case, he can state “with a high degree of medical certainty” that Floyd did not die from a drug overdose or a primary cardiac event.

Philonise Floyd, George Floyd’s brother, took the stand later Monday afternoon.

“On May 24th, I got married, and on May 25th, my brother got killed, then my mom died on May 30th,” he said early in his testimony when explaining how the month of May remains a difficult time for him. Asked to detail what role his brother played in the household when they were younger, Philonise reflected on the impact George’s leadership had on his family.

“He was so much of a leader to us in the household,” he said. “He would always make sure that we had our clothes for school. He made sure that we all were gonna be to school on time. … He was one of those people in the community that, when they had church outside, people would attend church just because he was there.”

Later, Philonise spoke on George’s relationship with his mother.

“He was a big mama’s boy. … Every mother loves all of her kids, but it was so unique how they were with each other,” he said.

After Philonise left the stand, Seth Stoughton—a law professor and former officer—was called to testify. Stoughton is known for, among other things, being the principal co-author of the NYU Press publication Evaluating Police Uses of Force.

Earlier on Monday, Hennepin County District Judge Peter Cahill denied a motion from the defense to sequester the jury due to the unrest following the police killing of 20-year-old Daunte Wright in nearby Brooklyn Center.