Remember that controlling law for this incident is Cayman Law. I am certainly not qualified to the bar here in Cayman but I would not come to any legal conclusions based upon court decisions elsewhere, including in the UK.
Some basic things to set straight:
1) This matter is under investigation by a detective with the Criminal Investigation Department (CID) of the Royal Cayman Islands Police. This does not mean than anyone has been or will be arrested, charged with a criminal offence, or face any sort of criminal trial. It is simply too early in the process.
The Criminal Investigation Department of the police force is called to investigate any death which may have the mere possibility to have some sort of criminal aspect - even if it is almost certainly not a criminal matter. So the mere fact that CID is investigating should not be taken to mean that the police think that charges will, or will not, be brought. They are simply the officers responsible for making the inquiry.
A decision to prosecute the DM, the shop, or anyone else would not come from the police. The police must submit their case and the prosecutor's office makes the decision to prosecute or not.
Often deaths in such circumstances are referred to a Coroner's Inquest. A jury hears evidence and can make a determination as to whether the matter is "death by misadventure" or something else. I would not be surprised if it took two years or more before a Coroner's Inquest takes place, if one happens at all.
2) The boat which discovered the missing diver was a fishing boat which was participating in a tournament. They alerted authorities and attempted to assist. They should be commended for their efforts in a situation which they suddenly and unexpectedly found themselves thrust into.
3) Cayman Law does require that a person remain on the dive boat while divers are in the water. I am no lawyer but as far as I understand there are no qualifications required of the person remaining on board. I have been told by a member of the Marine Conservation Board that the person remaining on board is not required to be capable of operating the vessel, using the safety equipment, or assisting with a rescue. I do not know for certain if this is true.
4) English is the common language of the Cayman Islands. All Caymanians speak it. Expatriates from non-English speaking countries must pass a test prior to taking up employment in Cayman. While there are some small areas where this policy could be abused (a French speaker from Quebec in Canada might not be tested) it is 99.9% safe to assume that the DM spoke English.
5) "DM's" in Cayman are almost always actually qualified to a minimum level of Instructor. That is the industry norm here. I am personally aware of only three persons who were hired for a dive job in Cayman with only a DM certification. They were working towards, and promptly completed, an instructor certification. Such advancement was an explicit expectation of their employment.
6) I have chased a diver to 150+ feet on a single Al72 tank and lived to tell the tale. I have previously recounted the story on this board. It was vigilance with a bit of luck that let me bring her up alive and uninjured. Suffice it to say that she failed to comply with explicit instructions which were a part of the briefed dive plan. There is no way I would have chased her to 300+ feet.
7) Local media is no better than elsewhere in accurately reporting watersports deaths. One local newspaper recently ran a headline with words to the effect "Woman dies snorkeling" when in fact the woman was out of the water and on a boat when she suddenly collapsed. Moreover, the paper was merely quoting the press release from the police and did no investigation of their own. Take home lesson is that not all watersports deaths are actually related to the person being engaged in a watersports activity.
On to pure speculation:
An oft asked question is how the diver managed to surface from 346ft. The obvious answer is that he somehow became positively buoyant. I can think of four ways that could have happened: 1) dropped weights, 2) added air to BC by power inflator or by mouth, 3) breathed the tank down and became positively buoyant without adding air to the BCD, 4) swam up in the water column until expanding air in his BCD carried him to the surface.
Options #1 or #2 required controlled voluntary action on the part of the diver. Option #3 could occur with an unconscious diver so long as his regulator was still in his mouth and he was still breathing. With option #4 some voluntary action is required but he could lose consciousness before surfacing.
