Mar. 2, 2012— -- On Feb. 23 Gabe Watson, the 34-year-old Alabama man some called "the honeymoon killer" after his wife died on their scuba-cruise honeymoon, had the murder charge against him dismissed by a Birmingham, Ala., judge.
Although the judge declared there was not enough evidence to continue his trial, the cloud of doubt and mystery still hangs over Watson and the events that took his wife's life.
In an exclusive interview with "20/20" anchor Elizabeth Vargas, Watson for the first time spoke publicly and in detail about what happened that day.
Unlike the other passengers aboard the Spoil Sport, including her husband, Tina Watson was not an experienced diver. She had 11 dives under her belt, none in open water.
Gabe Watson said she never told him this last fact, adding she wasn't nervous.
"She was excited," he said. "I was excited. We were ready to go."
Watson expected a relatively easy dive.
"I kind of figured, We're on vacation. They're going to be very easy, calm, nice, pretty dives," he said.
In fact, the dive was a 50-foot wreck dive to the SS Yongala, a 350-foot steamer that sank in 1911. And there was a strong underwater current, which led the crew to label it a red dive, i.e., one typically for advanced divers only.
The couple planned to travel down the anchor line, drift across the top of the wreck, pick up a second line and return to the surface.
Within minutes, the severity of the current hit Gabe Watson.
"As soon as we let go," he said, "we were moving, moving quite a bit. ... It was definitely not what I was expecting, and neither was Tina."
Tina Watson looked at her husband and motioned back toward the anchor line, Gabe Watson said.
"I stuck out my right hand, she grabbed it with her left, and we both started swimming back to where we came," Watson said.
The current prevented them from making much progress, he said.
"I turned to her, grabbed my inflator hose and motioned to her, you know, Fill it up, thinking that she's going to understand. Put some air in your [buoyancy compensator] and we'll start floating up," he said.
"Nothing happened from the inflator hose," Watson continued. "That was when I realized, you know, We're -- This isn't good. We're in trouble. So I reached out and grabbed ahold of the b.c. strap right there. And I just pulled her in, and then I turned and started heading back to the anchor rope."
"I was scared to death," Watson recalled.
He turned back and tried to yell, "Swim! Swim, Tina, swim!" he said.
"All of a sudden I just felt this whack across my face, and my mask got, like, turned off to the side of my face," he said.
Gabe let go of Tina to replace his mask, he said.
When he turned around to look, Tina was 10 feet down and sinking, he said.
"She was face up, and she had her arms up. She was reaching out for me to grab ahold of her."
"I kinda just turned on my head and gave a few kicks down to see if I could grab her," he said. "And she was still out of arm's reach. And that -- I just decided I got to go find somebody."
How could he leave his wife?
"I don't think I was making rational choices at that point," said Watson. "I don't know what I would have done had I stayed with her. I don't know that there's anything that I was actually capable of doing."
Watson ascended in a controlled way to avoid injury, as with any scuba dive. At the surface, he yelled for help, and a dive master raced to find Tina.
He brought her up, and crew members and fellow passengers tried to resuscitate her for over 40 minutes while Gabe was comforted by other divers on another boat.
Why didn't he go to the other boat?
"That's not something I can handle," Watson said. "I don't ever want to see one of my loved ones being worked on like that, ever."
John Downie, a cruise passenger who is a doctor and who tried to help Tina Watson, told Gabe Watson his wife was dead.
"I just-- I just collapsed onto him. ... We just all kinda piled into each other and at some point fell to the floor. And I don't know how long that went on. I -- I mean-- I was devastated."
When Australian police interviewed Gabe Watson for details on what happened, it became more of an interrogation. Fellow passengers came forward, saying Watson's story didn't add up. Police started comparing it to the dive computer.
Dr. Carl Edmonds is a diving medical expert who has examined this case and was prepared to testify for the defense. He said that, in the context of diving accidents, Tina's death was neither mysterious nor suspicious.
"She was doing a dive to a depth that she had never been to before, in conditions she'd never experienced before," Edmonds said. "It all fits together ... as a very common drowning accident."
'Honeymoon Murder': Scuba Experts on Tina Watson's Death
Michael McFadyen, another diving expert who has examined this case and was prepared to testify for the defense, agreed. He said he wouldn't take Tina Watson or any diver with her lack of experience on the Yongala dive.
"She's never been [scuba diving] in the ocean, never been in salt water, never been in a place where there's wave actions, currents," he said.
Edmonds and McFadyen said the first three to four minutes of Tina Watson's dive were normal, as she and her husband leisurely followed the anchor line down 30 feet to the Yongala wreck.
It was in the fifth minute, when they let go of the anchor line and Tina Watson began to sink involuntarily, that the touble began.
"[Sinking this way] makes you very unsettled," McFadyen said. "It also makes you swim in a vertical situation instead of being horizontal, like you should ... which takes a lot more effort."
Edmonds said that Tina Watson's motioning back to the anchor line was "sensible, except it doesn't take into account the effect of the current. ... Had they got back to the line, it would have worked. Unfortunately, they only got halfway back."
"Because she was over-weighted, because she was swimming against a current, she's exerting herself greatly," Edmonds said. "And we know that, because of her air consumption, which was unbelievably high, she was also panicking."
Panicking made her overbreathe, then aspirate water through the regulator in her mouth, eventually losing consciousness and sinking to the ocean floor, Edmonds said.
"The autopsy was very clear," Edmonds said. "The findings were that she [was] drowning and that she had air embolism. ... If you look at the statistics on diving fatalities, the two commonest causes of death are drowning -- in about 70% -- and air embolism -- in about 14%."
The prosecution said Gabe Watson didn't ascend as quickly as he might have, and that this showed his intent to kill his wife.
"I happen to think that he went up quicker than they think he did," McFadyen said, "mainly because they're relying on the ... the graph that's produced by the dive computer as being 100% accurate, and it's not."
Dive computers take snapshots of a dive based on each time a diver goes through a 10-foot level, McFadyen said. "So if you go through at two minutes 10 seconds, it would record it as two minutes. If you went through at two minutes 59 seconds, it would still record it as two minutes. So it's not exact."
Because of this, McFadyen believes Gabe Watson ascended the 54 feet in about one minute 30 seconds, an ascent he characterized as "quick."