Testimony continued in the murder trial of former Minneapolis police officer Derek Chauvin, who is charged with second-degree murder, third-degree murder and second-degree manslaughter in George Floyd’s death. A medical expert testified Thursday that Floyd died from a low level of oxygen that damaged his brain and caused his heart to stop. Dr. Martin Tobin, an expert who specializes in pulmonology and critical care, was the first witness called to the stand on the ninth day of the trial. Emergency medical physician and forensic medicine specialist Dr. Bill Smock later took the stand and gave a similar opinion, saying Floyd died not of a drug overdose, but because he had “no air left in his body.”