Now to address some of the other posts ...
To me, the single most damning evidence against Gabe is the slow ascent. I consider myself a decent diver. I think I can follow my training. Even so, if my new bride, who took up scuba diving at my behest, got in trouble on a dive and I needed to get help, I expect I would handle it as a CESA rather than as Gabe seems to have done. Under the circumstances, the slow ascent gives me a lot of trouble.
I think this is can be described as an element of "planning". Gabe's claim that he made a fast ascent to get help is shown to be a lie by his own computer. If he did not intend to kill Tina, then he should have done exactly what he claimed and he knew he should have at least gone to the surface as quickly as possible for help as a minimum to help save Tina.
I see other elements of planning as well:
Aborted first dive, claiming the computer was beeping and the battery was in backwards. After establishing that this cannot happen, if I were a juror, I would classify it as a lie, which woud mean Gabe has no credability on the issue. In addition, a friend of Tina's described how, when Tina and Gabe were packing for their trip, Gabe's computer would not work and he discovered he had put it in backwards and Tina and her friend teased him about it. He got it working properly again that night. I would not classify it as a coincidence that Gabe claimed his computer battery was in backwards a second time on the fateful day. First, once he had fixed the problem at home, why would he mess around with it again and put it in wrong again? I would feel the more reasonable explanation would be that this is how he got the idea to make the claim on the first aborted dive on the day Tina died. Then I would classify it as intent and planning as his effort to separate him and Tina from any other witnesses.
We know Gabe asked to Tina to increase her life insurance at her work and make him the beneficiary. We know that he made the statement to Tina's friend that for just $10 more, Tina could have a one million dollar life insurance policy. This was before the trip, but after the trip, at Tina's funeral he said to multiple witnesses that she
could have had a one million dollar policy. So, his knowledge of this possibility and his thoughts about it are well-established. Did Gabe do the same for Tina on his life insurance? Did he or anyone else ever talk about how much life insurance he could have had for Tina to collect? Somehow, I think not. We know he attempted to collect on her life insurance at work, but he was not named the beneficiary. What was the conversation with the insurance company? I'm sure they have to keep some kind of record of the call or calls.