Florida medical examiner Dr. Thomas Beaver was tasked with finding out exactly what caused Canadian Sharkwater director filmmaker’s death in January 2017. There are only a handful of reasons that someone can die while diving. 

Many of them could be eliminated immediately by Beaver: Stewart didn’t run out of air or get entangled in some object and drown. Beaver quickly determined from his autopsy that Stewart didn’t have any medical reason which may have caused his death: he didn’t have a heart attack, there was no evidence of a brain aneurysm, he had not used any drugs that might have triggered a fatal event underwater. 

That left four potential causes of death, which he narrowed down to hypoxia, an acute lack of oxygen which he explains in the video above.

Dr. Beaver adds that there is a wild card in his diagnosis. The crew that recovered his body performed unauthorized “forensics” before handing the body over to the Coast Guard. That makes Beaver uncertain about how that might have changed the evidence. He also states that his diagnosis of hypoxia does not match the scenario perfectly but in his opinion is the best fit for the symptoms that the two men displayed.

To learn more about Stewart’s final dive, watch The Third Dive.