Mystery in the deep blue sea

Divers from across the world continued to dive the wreck of the Yongala day in and day out, but onshore, Australian authorities were still troubled by the death of the young American honeymooner there months before.

The police seemed to have an easy set of facts before them: a marginal novice diver in over her ability who then panicked and drowned. And yet, they could not rule that death accidental.

The matter of Tina Watson remained an open investigation.

And the question that would not leave the investigators' minds was this: had she died as a result of foul play?

This question police were asking was not much different than the one posed by the dead woman's father back in Alabama.

Tommy Thomas: I would like to know exactly what happened. The two of them went in the water together and he came up without her. A lot of this doesn't make sense.

The Australian police advised Tommy Thomas to involve his own local police force on the case.

And that's how detective Sgt. Brad Flynn of Helena, Ala., became involved in a case 9,000 miles away. The dead woman's father asked for help in understanding what was shaping up as a mysterious drowning on the Great Barrier Reef.

Dennis Murphy, Dateline NBC: What was he asking you to do?

Brad Flynn: Find out what happened to my little girl.

The Aussies, he learned, were looking askance at the husband, Gabe’s, story.

Det. Flynn, who doesn't dive, who'd never been to Australia, was able to quickly get past the Down Under lingo and speak to his counterparts there in the international language of police procedures.

Det. Flynn learned that his counterparts in Australia were looking askance at the husband, Gabe’s, story.

Brad Flynn: And it was after they had spoken with him that they started kind of raising their eyebrows a little bit and saying, "I think we need to look into this a little bit more. Some things just aren't -- I don't get a good feeling with this."

What was perplexing the authorities down there was not just Gabe’s story, but the story told by a dive computer, a vital piece of gear for any scuba diver. When you learn how to read it, it will tell you critical information, like how deep you are, how many minutes of air you have left. And it does something else: a memory chip inside will describe the dive you've just made when you return to the surface. If you went down, say, 60 feet, this thing, the dive computer, will show you exactly that.

(Police tape)

Gabe Watson: Just turned and kicked and shoot straight back ... right up to the top.

Gabe's problem was that the story he told of his dive with Tina, didn't match the dive recorded on his computer.

Gabe aborted his first dive that morning with Tina. When he got under, he said, his dive computer started "beep beeping" a malfunction. The two had to surface.

Brad Flynn: This is where red flags start popping up. His statement was that when he got back to the boat, he realized that the batteries were in backwards.

(Police tape)

Gabe Watson: I pulled the battery out, swapped it around, hooked it back up…

Brad Flynn: I've never seen any electrical device that operates whatsoever if the batteries are in backwards.

The Australian police tested that common-sense theory and, sure enough, with the batteries put in backwards in Gabe’s dive computer, the thing didn't work at all. There would have been no underwater "beeps" and that aborted dive wouldn't have been recorded at all.

But it had recorded the first dive. It showed Gabe going down a few feet, then coming back up.

Brad Flynn: It registered. It was downloaded. The information from that dive was downloaded by the Queensland police.

Dennis Murphy: So if this dive computer is working, but he tells Tina, "We've got to go back up.” Why would he do that?

Brad Flynn: That's the million-dollar question. Gabe and Tina were the only two people there. And we're having to backtrack to fill in the pieces here.

So now the cops were comparing the statements made by Gabe in his video with the statement made by the dive computer, and they weren't matching up.

This is how Gabe described his desperate attempt to reach Tina as she fell to the bottom.

(Police tape)

Gabe Watson: I went down. Started kicking down and I was kicking down but as fast as I was kicking down to go get her, she was ... she was going down just as fast.

But the dive computer said that never happened. It showed no attempt to sharply descend after Tina.

And it also contradicted his account of bursting to the surface after he'd made the decision to go for help ASAP.

(Police tape)

Gabe Watson: So from that point, I just ... I pretty much just turned and pretty much just rocketed to the top and, you know, I'm amazed that I didn't end up with the bends or something.

But the dive computer recorded a downright leisurely ascent:

Brad Flynn: It took him over two minutes to cover that distance.

Dennis Murphy: To go 40 feet?

Brad Flynn: Forty feet.

Seasoned divers say that's a snail's pace. A safe ascent from that depth could be made in 45 seconds to a little over a minute.

Brad Flynn: To say that it's slower than his bubbles were ascending is-- is truly an understatement.

Compare Gabe’s recorded rise with that of the dive instructor who pulled Tina off the bottom. Even carrying her, the instructor was able to ascend 100 feet in a minute-and-a-half, while Gabe’s recorded ascent of only 45 feet took between two and three minutes. It's a pro's skill versus a recreational diver's, but still -- police said when you factored in the guy was after all supposedly getting help for his wife, 45 feet, five deep ends of the swimming pool?

Brad Flynn: It's been red flag after red flag after red flag. And if he did what he said he did, we should be able to verify that. But every step that we took, we found more differences, more things that we could not explain, that he couldn't explain.

And there was another red flag: this videotaped statement was made at Gabe’s request.

It was about the water current by the Yongala.

(Police tape)

Gabe Watson: I just can't help but think that that the fight against the current is what allowed whatever thing took place that caused her to black out or whatever, and sink.

He'd bought a book at the local aquarium, researching the prevailing currents, and he told the police he was now sure that they at least partly explained Tina's drowning.

(Police tape)

Gabe Watson: We still don't know what physical thing happened with her. You know, I keep thinking you know had the current not been there, you know we'd still be out on the boat diving.

Brad Flynn: In his first statement, they ask him, on a scale of one to 10, what was the current like? He says, "a five." He said, "if it would've been much stronger, I don't think a novice diver," implying Tina, "would've been able to handle it." Several days later, he shows back up at the police station .

(Police tape)

Gabe Watson: We both realized once we both got in the current that that's too much.

Brad Flynn: He starts talking adamantly at how severe the current was.

Dennis Murphy: So he's researched the current?

Brad Flynn: Yeah. After the fact.

(Police tape)

Officer: Just tell us what it is...

Brad Flynn: If somebody shows back up, unrequested at my door, I’d like to talk to you about something I didn't mention before, is that going to cast suspicion? Absolutely.

Dennis Murphy: Is it possible that he's telling stories that sound nonsensical just because he's in an emotional panic and knowing that, your story's going to get jumbled up.

Brad Flynn: I can see that, but there are other parts of it that either he's told either the police or other witnesses that draw suspicion, even after the initial shock has worn off. And it should be clear in his mind what happened.

Dennis Murphy: The story's getting amended?

Brad Flynn: Yes. Changed after the fact.

And investigators knew that Gabe was certified as something called a "rescue diver." He'd taken a course in how to assist panicked and unconscious divers from under the sea. And yet, on that day, he'd opted not to go for his own bride.

And why couldn't police verify Gabe’s story that before he surfaced, he tried to alert other divers at the descent rope that he was in distress?

(Police tape)

Gabe Watson: I saw the people, I went up to them, you know, it was like grabbing a hold of them shaking them.

Brad Flynn: The problem is we've interviewed everybody on the boat. Nobody says they encountered Gabe underwater doing that.

Gabe Watson was becoming a suspect.

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