K_girl, as I've stated before, the only "personal reasons" I have behind anything I've written are that I have taken an interest in this case and seem to see it from a different perspective than most other people do. Maybe I just enjoy playing devil's advocate, I don't know.
Devil's advocate? Hardly. Feels more like a bad take on a Monty Pythin skit to me.
Many of the comments you made or quoted sound like they came from people who weren't actually aquainted with the story. Put forth any fact you like and let's discuss it. Your shotgun approach makes it hard to address anything and move toward consensus.
How about this. You have a scenario with visibility where you haven't lost sight of your buddy, she has fallen a few meters below you, and she is in distress and sinking. You are at the start of your dive with a full tank and no issues of your own. Is it the right thing to let her sink, lose sight of her, and swim for help, or to vent some air and get down to her? Remember, you're rescue certified.
If, for some insane reason, you decide that leaving your buddy to go for help makes more sense, where exactly do you plan to send the help? Now that you've lost contact in current and she probably won't be anywhere near where you last saw her, where do you look? If Watson were also a new diver, was in some distress himself, saw her dropping into a depth he couldn't handle, or lost sight of Tina, then searching out assistance was probably the right thing.
If Tina was having breathing difficulties, it would most likely have been related to panic or hyperventilation. She had a full tank of air and her regulator never left her mouth. Give me any other reason why she might have been unable to breath without having her tank valve closed for a minute or two that also would not have shown up in a post mortem investigation. A panicking diver could definitely be dangerous up to the point where she lost consciousness. A hyperventilating person is typically just about incapacitated and should be easy to control from the start.
All this discussion assumes that Watson actually wanted to save Tina, who was having some problem that he did not cause. If one wants to believe that to be true, then all of the actions and facts have to support that. While it is possible, I don't believe it to be true. Among the tipping points for me is the dive computer battery story.
Among the pieces of information I have been hoping to hear from the start of this is just how capable a diver Watson was. We know he was rescue certified, but not if he had any more advanced certs or what his diving history was. At least, I don't recall that ever coming out. If it turns out that he had the minimum dive count required for his certifications and wasn't really capable, I would be more likely to believe he was incompetent rather than a murderer.
Also, with the facts in play, I can't see how anyone could say that Tina died "as a result of a diving accident for which she was solely responsible." This woman was apparently heavily pressured into diving at all by her fiance/husband and then taken, by him, on an inappropriate dive for a beginning diver. In a vacuum, we would all put blame on her for even getting into the water, but it would be quite hard to name her as "solely responsible" under any circumstance. A statement like that is purely inflammatory and has nothing to do with the concept of "devil's advocate". If I were to name her as solely responsible, it would be for trusting her safety to a man who either wasn't as competent as he claimed, or who actually intended her harm, not for her actions in the water.
Also, as far as your question about why he would go back to Australia if he were guilty, there are a couple answers to that. One is that there was some discussion ahead of time that he would be allowed to plea the case out and get off with a short sentence. For a man who was actually guilty, taking a year to erase any possibility of a future finding against him seems a good deal. It effectively brings an end to any investigation. Second, with extradition proceedings continuing, it could have reached the point where his return to Australia was inevitable. At that point, a cooperative defendant stands a better chance than one dragged back kicking and screaming. This is proven out in the judge's comments on the case.