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MIAMI (CBSMiami) – The family of a filmmaker who died while diving in the Upper Keys plans to file a lawsuit in his death.

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Rob Stewart was a well-known conservationist and documentary film maker.

He died on a dive off Islamorada in January after trying to shoot video of an endangered sawfish shark.

His family is suing for negligence. Attorneys claim he died after making a 3rd deep water dive to help retrieve a piece of equipment.

“Peter Sotis and the Horizon dive captain decided they had to get a $15 grappling hook,” said Stewart family attorney Michael Haggard.

The family alleges Sotis, from ADD Helium, was on that dive with Stewart. They said Sotis was his instructor who trained him on a dive apparatus known as a rebreather.

Attorneys said when the two resurfaced, Sotis got out of the water first and passed out. While people on the boat attended to him, Stewart sank to the ocean floor.

CBS4 tried speaking to Sotis, but his staff said he was not in.

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An attorney speaking on his behalf said Stewart volunteered to go on that final dive to retrieve the equipment.

“Rob Stewart volunteered to go. Peter Sotis told him that was not necessary,” said David Concannon, an attorney speaking for Sotis. “Stewart volunteered again, and Sotis said again no, that’s not necessary, but Stewart insisted.”

“We know the rules as an instructor – you never leave your student in the water,” said Rob’s father Brian Stewart. “The self-interest of Peter Sotis is why Rob is dead right now. It’s all about him.”

The attorney goes on to say that, unknown to Stewart, Sotis adjusted the gas mixture levels of the equipment.

“Peter Sotis was manipulating the gas levels on the dive computer to accomplish more aggressive decompression profiles because in his words, he was the best in the business,” Haggard said.

Also named in the suit, Horizon Dive Adventure, the Key Largo company that provided the boat and crew.

Through their pain, his parents are trying to concentrate on Stewart’s message of conservation and preserving the ocean.

“He had a belief that if he could teach people about nature and living in harmony with nature the world would be a so much better place,” Brian Stewart said.

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As the case winds its way through the court system, the Stewart family plans to complete the project Rob Stewart was working on when he died. They hope to debate his film in the Caine Film Festival next year.