Carl Cuthbertson’s wife Diane, 59, stopped breathing as she ascended from a WW1 wreck off Flamborough Head last August, a coroner found.
The police found no evidence of foul play, said Prof Paul Marks, who concluded her death was accidental.
Mr Cuthbertson, who has made a formal complaint to Humberside Police, only received his wife’s body back for a funeral in April.
He said the shock of discovering he was being investigated seven months into their inquiries added to the struggle to come to terms with his wife of 40 years death.
He said: “It was a shambles, an exercise in frustration. The worst thing was that there was no communication or explanation of what was going on. We were kept in the dark all the way along. Their original statement was that there wasn’t any criminality. You think who have they been knocking on doors talking to? I am squeaky clean, I had no reason to do it.”
Mr Thompson, diving officer of the Filey Brigg Diving Club branch of the Sub Aqua Association, also discovered last November after an inquest into the mother of two’s death was postponed that he was being investigated by police. Mr Cuthbertson said: “After Paul, they decided to also investigate me. They could have come and had a chat and seen my records which showed I had no reason to do anything, but they decided to do it covertly.”
The inquest heard that Mrs Cuthbertson, the owner of the Tot Shop nursery in Driffield, took up diving, after taking her son Adam to do a course. Diving became a passion and she went on to complete 80 to 100 dives. She was “buzzing with excitment” about the dive due to take place in ideal conditions on August 16 last year.
Mr Thompson told the hearing they made a “nice, steady” ascent after an uneventful dive, when she grabbed one of his chest straps at around 16m. They continued up together, with him facing her, but then at 4m she gave the “out of air” hand signal.
He handed her the demand valve, which divers breathe through, from her second independent cylinder and noted her guages showed air in both cylinders. But she again gave the “out of air” signal. He told the hearing he then gave her his spare, but she continued to signal out of air.
He said: “I thought at the end of the day I haven’t the air to give her - the only place she is going to get air is on the surface.”
He broke down as he told the court that when they broke surface and he removed her mask her eyes were fixed and her lips were blue.
Prof Marks said Mrs Cuthbertson had stopped breathing for an unknown reason. She could have panicked or held her breath. The rapid ascent then caused pulmonary barotrauma, or damage to the lung from rapid pressure changes. Mr Thompson, who surfaced at the same rate, escaped injury. Afterwards Mr Thompson said it had been a “very stressful nine months” adding: “Carl has been good and we have supported each other. The hardest part was that Diane was a friend.” Humberside Police said: “It would be inappropriate to comment as a formal complaint has been made and is subject to an internal investigation.”