I have left my home in Sydney, Australia and with my wife Kelly, we are on our way to Birmingham, Alabama's largest city. I am to appear at a murder trial that started a few days earlier. It centres around an alleged murder that I did not witness, a victim I have never knew and a defendant I have never met. How did I get involved?

For almost 25 years I have been an avid scuba diver. I dive every week of the year if the weather permits, sometimes as many as four times a week. Since 1988 I have completed 3,249 dives in locations as diverse as Norway and Tasmania, New Zealand and Papua New Guinea. Not only am I a diver, I also have published a web site - Michael McFadyen's Scuba Diving - since 1995. This web site is totally funded by me and contains articles on the hundreds of dive sites and shipwrecks I have visited all over the world. My web site is there to pass on my knowledge to other divers.

Since I became a diver I have been interested in dive accidents, how and why a diver gets into trouble and, in some cases, dies. I have attended inquests into deaths and written about them for dive publications. I have also investigated other incidents and reviewed well known incidents. All this information I have made freely available to divers in the hope that they will not make the same mistake. Some of the articles I have written have appeared in various publications as well.

On 22 October 2003, a visiting US diver called Tina Watson died when diving the wreck of the SS Yongala off Townsville, Queensland on her honeymoon. The story that emerged from this incident via the media made me think that her husband, Gabe, had probably had an active part in her death. The main reason for this was the report that Gabe claimed that his dive computer beeped at him on his first attempt to dive and when he checked the computer, he found the batteries were in back to front. Like other divers I know, Kelly and I ridiculed this statement. A dive computer cannot beep if the batteries are in backwards.

As well, some of the other aspects of his story as reported by the media did not make sense. Of course you can chase sinking divers and catch them. Of course a rescue-certified diver should have the skills to save someone.

Then, in 2007 and 2008 an inquest was held during which where damning allegations were made by the police of a witness seeing Gabe "bear hugging" Tina after allegedly turning off her air. The police came up with the theory that he used the faulty computer story to return to their dive boat and then re-enter the water later, to isolate Tina and himself from other divers so that he could kill her. His apparent "lie" about the computer was then used by Police to say "well, he lied about this, so he must have lied" about other apparently inconsistent statements he made.

After reading everything that was published in the media, "Guilty your honour" I thought. Eventually, nearly 5 years after his wife died, Gabe was charged with murdering Tina and in 2009 he came back to Australia to face trial. Instead, he pleaded guilty to manslaughter and was jailed for 18 months.

Back in August 2010 and I am deep in the Australian Outback. On the radio I hear an interview with Lindsay Simpson, one of the co-authors of a book about the murder. In September I got home and did some internet searches. I found transcripts of Gabe's second interview with the Queensland police. I began reading it and before I had gone halfway through the transcript of the first tape recording, I was stunned. He is not guilty. He has been telling the truth but the police have ignored what he has said or just did not understand it.

The statement that has convinced me is one where Gabe advises the police interviewing him that the reason for the beeping computer was the fact that his transmitter that sends the pressure reading from his dive tank to his computer has failed because the battery [he didn't specify which in his not terribly articulate answers to police] was in back to front. The police have probably just not understood that his computer actually consists of two parts, the transmitter and the wrist module, each of which take a separate battery. I decide to add a page to my web site on the incident, outlining my theory. I have it up within a few days, but as I have no access to other information, it stays fairly simple.

For Christmas 2010, Kelly gave me a copy of the book, Honeymoon Dive. Over a camping trip after Christmas I read the book. Kelly also read it and we came to the same conclusion. Gabe is innocent and he has been telling the truth. It is the additional information in the book that has convinced both of us that a grave injustice has been done on this matter. I use some of the information in the book to update my web page. However, while it is a lot better than it was, I still do not have the information to make it conclusive to others, especially non-divers.

July 2011 comes and there is an article in the Sydney Morning Herald by Jennifer Cooke, the other co-author of the book. She has interviewed Dr Carl Edmonds. Carl has written all the dive medical text books and is considered the dive medical guru by divers. He has basically said exactly what I have said about what happened and how Tina Watson died. I try to contact Jennifer to see if I can get more information but I have no luck in finding an email address for her.

A few weeks later Jennifer emails me. She has found my web site and decided to contact me. She is coming to Sydney from outside Washington where she currently lives and wants to meet me during her visit and talk about the case. On 2 August 2011 we meet. Jennifer tells me that despite the police case apparently pointing strongly towards Gabe's guilt, once she went through the evidence of the police case she always had doubts.

She had been a court reporter for three decades as well as having served as a jury foreman on a criminal trial and she could not believe that there was evidence in what she had seen that could prove murder beyond reasonable doubt. The alleged motive was weak or non-existent as well as being hearsay legally. But it had been difficult to get past the slant of the police case and Coronial finding without more expert knowledge on other diving accidents and deaths, as well as recreational diving in general.

She had since found that with Carl Edmonds, and now me. She wanted to meet me in case there was a possibility of us helping one another. There had been a very short deadline for Honeymoon Dive and there were issues she thought could be explored in more depth, particularly if the book needed updating should Gabe Watson be charged with murder in the United States, as the Attorney-General of Alabama seemed bent on achieving.

Of great concern to her was a page of testimony at the inquest referring to the separate batteries that went into the dive computer wrist module and the transmitter. If the battery was inserted into the dive computer correctly but the separate battery in the transmitter inserted incorrectly, it would beep a gas alarm - just as Gabe Watson had told police had happened. There was no other mention in any of the police brief or at the inquest itself of the transmitter. It was brought up in evidence only once - by Gabe's barrister.

We meet again a week later and Kelly comes along as well. Jennifer decides to give me some of the evidence that she has access to and I download onto my computer a lot of evidence that I have previously not been able to see. I start reading it. There are something like 1500 pages alone in the inquest transcript. I do not get far into reading it before I am gobsmacked to learn that the investigating police seem to not only have no knowledge of recreational diving, but have deliberately misrepresented evidence to the coroner. The main problem is that Dr Stanley Stutz, the witness they claim who saw Gabe holding Tina in a "bear hug" never actually said this. They had taken his comment about how the diver who brought Tina back to the surface was holding Tina (in a "bear hug") and started using it to refer to how Dr Stutz allegedly saw how Gabe was holding Tina (in a short "embrace").

It gets worse. The police divers appear to be either incompetent divers, with little knowledge of diving, especially recreational diving, or liars. Some examples are the claim about the tanks that are the most commonly used throughout the world, that "nobody would use them as they are too big" to not knowing how to read decompression tables. In addition, one of the police divers says it is impossible to do a series of tasks underwater which he claims Gabe said he did. The problem with this is that Gabe never said he did the tasks that the police diver attempted. Another problem is that later, both Kelly and I easily achieve these tasks on the first attempt. How much of an expert diver can he be?

I had started updating the single page and soon it had grown to four pages. These pages are about 6,000 words each. I add more and more information, and once back home, Jennifer gives me access to more evidence so I can explain to her any issues I see from a recreational diving perspective. The Queensland case and the inquest are looking worse and worse, I am starting to be embarrassed about what has happened.

Eventually I have updated the web site with all the information I have access to. I decide to start digging deeper into the information I have. I decide to try to work out things like how much air Tina used and a timeline of all the divers involved in what happened.

Working out the air consumption is important as it is a good pointer to the strength of the current and if Tina was panicking as I suspect. I am astounded to see that the Police appear to have not already done this and then to see that her average consumption for the dive is over four times what I would use.

The next thing I discover is that the only eyewitness to part of what happened, Dr Stanley Stutz, could not even have been under the water when Gabe and Tina parted. I had always suspected that what he saw was not Gabe and Tina, but this is confirmation to me.

I add some graphs and tables to show these new revelations.

Jennifer asks me one day what am I going to do with all this information. I respond that I have no idea, but I would like to somehow let Gabe's lawyers know about my web site. She agrees to pass on the email address for Gabe's father. I email him and tell him about the page I have on my web site. He responds that he was "already aware of my writings".

Over the coming months I refine the pages, adding more information as I continue to trawl through the inquest papers and a few witness statements. I am more convinced than ever that Gabe is innocent.

In November 2011 I am contacted by a private investigator working on behalf of Gabe's lawyers. The court has approved an independent investigator to look at the evidence and he has been allocated this task by the lawyers. He calls me a few days later and we talk for well over an hour.

I am then asked if I will appear at the trial as an expert witness. This is an unexpected twist in the saga! I had never thought that it might come to this. They tell me that Carl Edmonds has already agreed to appear. I think about it and decide that probably no-one outside Gabe's lawyers knows the evidence as well as I do and certainly no experienced diver has the knowledge of the case that I do. It would be impossible to find someone else that could come up to speed with the intricacies of the case in the time left before the trial starts on February 13.

I advise that I will attend. I will have to take leave from work but at least my expenses will be paid.

Things move along quickly now. I am sent a hard drive containing all the evidence that has been gathered by the defence team, including all the prosecution's evidence. There is an enormous amount of information here. There are statements that I have been dying to see. These clarify things that I had only previously guessed and make my air calculations even more conservative when I notice that the Police divers did not even correctly report the size of Tina's tank (and nor did they correctly report the size or model of her BCD).

Over the first four weeks of January I work with Carl and Gabe's lawyers, preparing questions to be asked of the dive related witnesses as well as pulling the Police dive re-enactments apart (they are later thrown out by the judge as being totally inaccurate attempts). In addition, Kelly tracks down the papers relating to the workplace prosecution over Tina's death. The lawyers have not been able to get access to this. There are some "silver bullets" here.

The third week in February 2012 approaches and Kelly and I head to Birmingham, Alabama. It is the second week of the trial and we walk into the court, past all the waiting media who of course have no idea of my involvement (well some do, but they have no need to approach me) and who start filming Gabe and his lawyers as they arrive at the court. We are introduced to Gabe and his new wife, Kim in the large underground courtroom. I am pleasantly surprised to find that I do not instantly hate him as I thought I might from what I have read about him. The trial resumes and we are soon heavily involved, writing questions on the go as witnesses give their evidence.

Over the ensuing days I find myself coming to like Gabe. His sense of humour is more Australian than American. He really seems to be a person who has been maligned by the press and others. His family is so nice as is Kim. I feel even more sorry for him and what he has had to put up with over the past 8 years.

There is a day off court so Kelly and I head out to the quarry in Pelham, south of Birmingham, where Tina and Gabe learnt to dive and where Gabe did nearly all his dives. Nikki Battiste, a producer from the US ABC 20/20 program takes us there and we meet up with Peter Patrick from The Age , who is also an experienced diver. Nikki wants to film me diving here and I have promised to give her underwater footage of the dive. I have already done (with approval) a 30 minute interview in front of three cameras with the anchor of the show, Elizabeth Vargas.

The quarry is huge and the water looks clean. We hire gear and walk to the water's edge. It is cold, but not too bad at 13°C. The quarry is also deep, over 42 metres in one spot. We do a 45 minute dive, reaching 25 metres. There are buses, trucks and cars as well as a couple of small sailing boats. There are also quite a few fish, many more than I thought there would be.

I have wanted to do this dive so that I could say at the trial that I had dived there. It confirmed my thought that the training and diving here could not give a diver the experience necessary to dive alone in the open ocean, especially on a dive as hard as the Yongala.

The next day we are back in court. It looks to us like the State is running out of witnesses. Already, nearly every one of them has ended up becoming a "defence" witness , because what they say in answer to questions from the defence was equally or more favourable to Gabe, than to the prosecution. It seems that the prosecution has not really done its homework and has not asked the witnesses questions that they should have anticipated the defence would ask. Most of these questions by the defence have shown up the ridiculous nature of the State's case.

At lunch I speak to a couple of the sheriffs. They tell me that they have never seen a capital murder case with such weak evidence. They say that they expect the trial will be over today. I have already thought that the judge will dismiss the case as there has been not one iota of evidence that Gabe murdered Tina - let alone planned it in Alabama.

As expected, after lunch the State rests its case. The defence then puts a motion for the case to be dismissed and for Gabe to be acquitted. After a very half-hearted attempt by the State to rebut this, the judge is scathing in his comments before acquitting Gabe. It is over. The court erupts clapping and cheering.

I am glad that it has been finalised, but in some ways it would have been better if Carl and I could have produced our evidence in court. Despite being acquitted, some people, including Tina's family, will not be convinced that justice has been done. If our evidence had received as much press attention as the State's theories, I was hopeful that many people would accept that Gabe was innocent.

A few days later, Kelly and I head off on a week's tour of the Deep South before our flight home. We speak to Gabe a few times and he sounds so relaxed. His Mum tells us it is the first time she has heard him laugh in over 8 years.

Later I put out feelers over a dive forum (where Tina's friends and family have been posting) to Tina's father offering for Dr Edmonds and myself to meet personally with them to explain how some simple known facts from both Gabe and Tina's air consumption prove that Tina was not murdered. These offers are either never passed on or taken up.

We eventually head home, happy that we have done the right thing and helped an innocent person escape a life in gaol.

To read about the death of Tina Watson and all the trials and tribulations of Gabe's battle with the Australian and US authorities, go to Tina Watson Death - Index of Articles.