George Floyd died from lack of oxygen

George Floyd died from a lack of oxygen during his arrest, a doctor at the trial of ex-police officer Derek Chauvin in Minneapolis has said. Contradicting the defence, Dr Martin Tobin said fentanyl did not cause Mr Floyd's death. He said even a "healthy person...would have died".

Mr Chauvin, 45, was filmed kneeling on Mr Floyd's neck for more than nine minutes during his arrest last May. The ex-officer is on trial for murder and has denied the charges against him.

The footage of Mr Chauvin, who is white, with his knee on African-American Mr Floyd's neck sparked global protests against racism.

The trial is in its second week and is expected to last for at least one month. The defence is due to begin arguing its case in court next week. The prosecution in the case of Mr Chauvin has now begun hearing from medical experts.

What did the experts say about fentanyl?

A toxicology report released last June said that Mr Floyd had the painkiller fentanyl and the drug methamphetamine in his system.

Since then, the defence has argued that the fentanyl caused Mr Floyd's loss of oxygen.

However Dr Tobin, an intensive care doctor, said that Mr Floyd's breathing did not slow down enough for the painkiller to have been a factor in his total loss of oxygen. Later in the hearing, the defence questioned Kentucky police surgeon Dr Bill Smock, who works for the Louisville police and is an expert in forensic emergency medicine.

Dr Smock said Mr Floyd displayed "air hunger", a term for when the body becomes desperate for oxygen. While a fentanyl overdose can slow down breathing, he said people who are overdosing are not aware that they are lacking oxygen and often appear sleepy. In contrast, he said Mr Floyd appeared to be alert.

On cross-examination, he concurred with the defence that there was "no safe" amount of methamphetamine to be in someone's system, and that an overdose of methamphetamine and fentanyl combined may look different from fentanyl alone.

Dr Smock also told the court that while viewing the footage, he heard Mr Floyd complain about being unable to breathe before he was restrained on the ground.