They chose to dive the popular yet difficult wreck of SS Yongala, a Passenger ship that sank in 1911, even though Watson had limited open ocean experience and Tina had never dived in the ocean or below 9 metres.
The dive company had also offered an orientation and guided dive with a dive master, which the couple had refused.
At around 10:30 am on 22 October, during an excursion from the dive boat Spoilsport to the site of Yongala, Tina lost consciousness and sank to the bottom, 30 m below the water's surface within two minutes of beginning the dive.
Watson claimed the currents were stronger than they expected and that he responded to a signal from Tina to return to the dive rope, where he noted a look of worry on her face before she accidentally knocked his mask and air regulator loose.
When Watson recovered his sight, Tina was sinking too quickly for him to retrieve her and he quickly surfaced to get help.
He also stated that an ear problem prevented him from diving deeper to help her and that there was nothing in his training as a rescue diver "about how to get somebody" in trouble to the surface.
Other divers nearby at the time, including Stanley Stutz, saw Watson engaged in an underwater "bear hug" with his "flailing" wife, after which he headed for the surface while Tina fell to the ocean floor.
One diver, Gary Stempler, photographed Tina by chance while taking a picture of his own wife that showed Tina in the background.
The photo showed her lying face-up on the ocean floor, something that did not come to light until a couple of weeks later when the pictures were developed.
Watson climbed aboard the Spoilsport and alerted dive instructor Wade Singleton, who brought Tina to the surface after ten minutes underwater.
She was taken aboard the adjacent dive boat Jazz II, where a doctor tried to resuscitate her for 40 minutes while Watson remained on the Spoilsport, but she was unable to be revived.
The day following the death, Tina's autopsy was performed by Professor David Williams, consultant forensic pathologist to the Queensland Coroner.
Williams found florid evidence of air embolism, but no degenerative disease.
He gave the cause of death as drowning.
Due to the unexpected nature of Tina's death and the implausible and conflicting statements given by Watson, the death was investigated by the State Coroner's office.
A coronial inquiry was held, as is the usual practice in Australia.
Watson had already left Australia by this point and declined to return, so did not testify during the inquest but gave evidence through his lawyers to the inquest and to the Queensland Police.
During the inquest, prosecutors submitted evidence that Watson's story contradicted the record of his actions stored by his dive computer.
They suggested the possibility that he turned off Tina's regulator and held her until she was unconscious, then turned the air back on and let her sink before surfacing himself.
As evidence, they described the many painstaking re-enactments of various scenarios conducted by police divers.
Tina's father claimed that Watson had asked Tina, shortly before their wedding, to increase her life insurance and make him the sole beneficiary.
1977
Christina Mae "Tina" Watson (nee Thomas) was born in West Germany on 13 February 1977, before relocating to the U.S. while still a baby.
1980
On 24 January 1980, she was legally adopted by Tommy and Cindy Thomas.
They lived in Walker County, Alabama, with her younger sister before moving to Louisiana then Birmingham.
2001
David Gabriel "Gabe" Watson met Tina while they were students at the University of Alabama at Birmingham, and they began dating in January 2001.
2003
Tina Watson was a 26-year-old American woman from Helena, Alabama, who died while scuba diving in Queensland, Australia, on 22 October 2003.
Tina had been on her honeymoon with her new husband, fellow American Gabe Watson, who was initially charged by Queensland authorities with his wife's murder.
Watson pleaded guilty to manslaughter and was sentenced to a term of imprisonment.
Evidence presented at the trial included Watson's differing accounts of what had happened on that day, of the couple's diving experience (or lack thereof), and of Tina's life insurance.
While Watson was serving his term in Australia, authorities in Alabama flagged an intention to charge him with murder at a later date.
After his release, he was deported to Alabama on the condition that he would not be sentenced to death if found guilty of murder.
Despite an earlier diagnosis of paroxysmal supraventricular tachycardia (PSVT), Tina began diving lessons in January 2003, and earned her certification just before her wedding to Watson on 11 October 2003.
Watson was purportedly a qualified certified rescue diver, with experience in the lake at Oak Mountain State Park.
Watson had completed 55 dives by the time of their marriage, and Tina 5.
The couple had planned a scuba trip in the Great Barrier Reef for their honeymoon, and flew to Sydney for a week before heading to Townsville.
2005
In March 2005, Watson launched legal action in Alabama's Jefferson County Circuit Court to recoup the cost of the couple's trip after the travel insurance company refused a payout.
He was seeking $45,000 for the accidental death plus compensation for trip interruption, medical expenses, phone calls, taxi fares, fees for extra credit card statements and unspecified punitive damages for mental and emotional anguish.
2008
The action was dismissed in May 2008 at Watson's request on the grounds the Australian investigation into his wife's death caused him "to reasonably apprehend that he risks self-incrimination in this case".
His Australian legal team believed "it was not in his best interest" to pursue the damages claim and his U.S.-based lawyer, Bob Austin, added that his client would not be voluntarily "going back to Australia."
2012
Watson was then put on trial, but on 23 February 2012, Judge Tommy Nail dismissed the murder case due to lack of evidence.
