The medical examiner who ruled George Floyd's death a homicide testified Friday that Floyd's heart disease and drug use contributed to his death, but police officers' restraint of his body and compression of his neck were the primary causes. Dr. Andrew Baker, who has been the chief medical examiner in Hennepin County since 2004, said Floyd had severe underlying heart disease and an enlarged heart that needed more oxygen than normal to function, as well as narrowing of his coronary arteries. Baker did not include a lack of oxygen, or asphyxia, as a cause of Floyd's death. Baker said that before he conducted the autopsy, he was aware that Floyd had become unconscious while he was in police custody and had died at a hospital. He said he did not look at videos of Floyd's death, including the bystander video that went viral, until after the autopsy was complete, so as not to be biased in his findings. Baker's findings were at odds with those of other prosecution expert witnesses who were explicit in their assessments that Floyd died from asphyxia. "In this case, I believe the primary mechanism of death is asphyxia, or low oxygen," said Dr. Lindsey Thomas, who retired in 2017 from the Hennepin County Medical Examiner's Office in Minneapolis. She said she reached that conclusion mostly from video that showed Floyd struggling to breathe. April 9, 202103:46 She testified Friday that she trained Baker and that they were friends. Thomas said she agreed with Baker that Floyd died from cardiopulmonary arrest — the ceasing of heart and lung function — complicated by the way law enforcement held him down and compressed his neck. The testimony from Thomas, a medical examiner of 37 years who works part time as a forensic pathologist in Salt Lake City and Reno, Nevada, as well as that of other experts Thursday, bolstered the prosecutors' arguments that Chauvin killed Floyd by kneeling on him for 9 minutes, 29 seconds. When Thomas and Baker testified, prosecutor Jerry Blackwell provided autopsy photographs of Floyd's body to jurors. The photos were not shown publicly. Chauvin's attorney, Eric Nelson, has said Floyd could have died from a heart condition or the fentanyl and methamphetamine that were found in his system. The testimony from several medical experts this week provided the first opportunity to hear how Nelson would argue that central point of the defense. He did that in part, on Friday, by posing hypothetical situations to the two medical examiners. He asked Thomas and Baker how they would have assessed Floyd's cause of death if the only information they had was either that drugs were found in his system or that he had heart disease, scenarios that would ignore the officers' restraint of Floyd and Chauvin's knee on his neck. Under cross-examination, Baker agreed with Nelson's statement that Floyd's heart disease, narrowed arteries and drug use "played a role" in Floyd's death, but he testified that those things did not directly cause him to die. "Mr. Floyd's use of fentanyl did not cause the subdual or neck restraint," Baker said. "His heart disease did not cause the subdual or the neck restraint." Thomas testified that such factors did not directly cause Floyd's death and that they are commonly included on death certificates for a "public health purpose." Under redirect by prosecutor Blackwell, who asked Baker what his opinion is as to Floyd's cause of death, Baker affirmed his findings that Floyd's death was a homicide. "My opinion remains unchanged," Baker said as his testimony concluded. "It's what I put on the death certificate last June. That's cardiopulmonary arrest complicating law enforcement subdual, restraint and neck compression." "That was my top line then," he added. "It would stay my top line now." Blackwell asked him whether he considered the other contributing conditions as direct causes of Floyd's death, and Baker said, "They are not direct causes of Mr. Floyd's death, that's true. They are contributing causes." In earlier testimony, other medical experts doubted Floyd's physical condition and his use of illegal drugs played a role in his death. Dr. Martin Tobin, a pulmonologist and critical care doctor in Chicago, also rejected the defense's claims Thursday that Floyd's drug use and underlying health conditions killed him. Tobin said a lack of oxygen resulted in brain damage and caused Floyd's heart to stop. April 8, 202101:58 "A healthy person subjected to what Mr. Floyd was subjected to would have died," said Tobin, a lung and critical care specialist at the Edward Hines Jr. VA Hospital and Loyola University's medical school in Illinois. Tobin said Floyd's breathing was seriously constricted while Chauvin and two other Minneapolis police officers restrained him. He said Chauvin's knee was on Floyd's neck for more than 90 percent of the time. Chauvin is on trial on charges of second- and third-degree murder and second-degree manslaughter. Police were called to Cup Foods, a convenience store, on May 25 after a cashier suspected that Floyd had used a fake $20 bill to buy cigarettes. A bystander video of Floyd, who was Black, saying he couldn't breathe as onlookers yelled at Chauvin, who is white, to get off him was uploaded to Facebook and widely viewed. It sparked international protests. For the first time, a seat designated for a member of Chauvin's family was occupied Friday, by a woman, according to a reporter in the courtroom. Her identity was not immediately known. Chauvin's wife filed for divorce shortly after Floyd's death.