(Minneapolis, MN) -- The doctor who pronounced George Floyd dead says the cause of death was oxygen deficiency. Testifying in the murder trial of former police officer Derek Chauvin, Dr. Bradford Langenfeld said Floyd arrived at Hennepin County Medical Center in a state of cardiac arrest, but noted that he did not appear to be having a heart attack. He added that insufficient oxygen can cause the heart to stop functioning on its own. Langenfeld also said there were no signs Floyd overdosed on a specific medication. Bystanders caught the incident on camera which had Chauvin with his knee on Floyd's neck for nine minutes. Chauvin faces three charges, including second-degree murder, in Floyd's death.