There are more dive details here:
Sister of Canadian filmmaker Rob Stewart, missing after Florida dive, says time is 'critical'
FROM THE ARTICLE
Stewart "resurfaced at the end of the dive, and as the boat was turning around to pick him up, he went back under — and was not seen again," Weaver said.
It's not immediately clear what caused Stewart to go back under water, but his sister said it was a "particularly difficult" dive, going to a depth of nearly 70 metres.
She said her brother may have lost consciousness after doing a third dive that day.
http://www.cbc.ca/news/canada/toront...sing-1.3961210
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