He told reporters on Thursday the debris was consistent with "a catastrophic implosion of the vehicle."
British Titanic explorer Dik Barton paid tribute to the work of his friend Nargeolet but noted issues raised with the design and maintenance of the craft.
"Everyone's wise after the event, but as we're hearing before, unfortunately there were many red flags flying here," he said.
He said sonar buoys used in the water for more than three days had not detected an implosion.
The Titanic sank after hitting an iceberg on its first voyage, killing more than 1,500 people aboard.
Persons:
moviemaker Cameron, John Mauger, Hamish Harding, Shahzada Dawood, Suleman, Paul, Henri Nargeolet, OceanGate, Dawood, Shahzada, Suleman Dawood, Dik Barton, Nargeolet, OceanGate's, Guard's Mauger, Moviemaker James Cameron, we've, Cameron, Stefan Williams, Michael Guillen, Joseph Ax, Steve Gorman, Charlotte Greefield, Edmund Blair, Andrew Cawthorne
Organizations:
Titan, U.S . Coast Guard, Stockton Rush, OceanGate Expeditions, British Asian Trust, University of Strathclyde, U.S . Navy, Navy, Wall Street, British, Reuters, University of Sydney, Thomson
Locations:
North Atlantic, North, U.S, Scotland, British, Greece, Canada, France, Britain, submersibles, Cape Cod , Massachusetts, St, John's, Newfoundland