Scuba shop owner David Swain and his wife of six years, Shelley Tyre, traveled to Tortola in 1999 for what was to be a romantic Caribbean getaway.

Only Swain made it home.

Tyre drowned while scuba diving in what authorities in the British Virgin Islands called an accident. They allowed Swain to take her body home.

Her parents sued three years later, accusing Swain of killing their daughter because he was romancing another woman and because the couple's prenuptial agreement denied him money if they divorced.

A civil jury in 2006 found Swain responsible and awarded her parents millions in damages, prompting Tortola authorities to reopen the case.

Now Swain, 53, who maintains his innocence, goes to trial on murder charges this week in Tortola, where prosecutors cite circumstantial evidence — including the damaged state of Tyre's scuba equipment and Swain's behavior after her body was found.

The murder allegations have rattled Jamestown, a cozy island town across a bridge from Newport, where Swain lived and sat on the town council after his wife's death.

"There's no question that people, the rest of the community, were in shock," said William Munger, a longtime Swain friend from Jamestown who continues to support him. "I think it's been difficult for many people in the town that know David well."

Swain's dive shop was a community staple that trained interested students. He wed Tyre, his second wife, in 1993 after bonding over an interest in scuba diving, and she began helping him with money to keep his financially struggling business afloat.

Tyre, also an experienced diver, was the middle school head at Thayer Academy, a college preparatory school in Braintree, Mass.

Swain and Tyre dove together on the last day of their March 1999 vacation to Tortola, a trip they took with another couple and that couple's young son. Swain surfaced about a half-hour later — but without his wife.

Christian Thwaites, the couple's travel companion, found Tyre floating on her back. The mouthpiece of her snorkel was missing, her mask was damaged and her fin was later found embedded in a sandbar — signs, experts testified, suggesting a violent struggle.

Swain called his in-laws from Tortola to break the news.

"'Shelley is no longer with us,"' Tyre's father, Richard Tyre, recalled Swain explaining matter-of-factly. "He had a hard time saying that she was dead."

When Swain returned to Jamestown, his face-to-face meeting with the parents was "heated," Richard Tyre said. While the parents initially thought Swain was irresponsible, they didn't suspect criminal wrongdoing. They presented the story anyway to J. Renn Olenn, a lawyer specializing in aquatic deaths.

Olenn visited Tortola, probed Swain's marriage and finances and consulted with diving and medical experts who concluded that homicide was the most plausible explanation.

Tyre's death certificate lists the cause of death as drowning and calls it "accidental unless proven otherwise."

The lawsuit went to trial in 2006 in Providence Superior Court, where Swain represented himself, only intermittently attended and was found liable after relatively brief deliberations. The jury awarded Tyre's family $3.5 million but Swain filed for bankruptcy and has not paid the sum.

He is now represented by Jeffrey Denner, a prominent Boston criminal defense lawyer who said he will show Tyre's death was a "tragic accident."

"This trial will bear no relation to the civil trial," Denner said.

The evidence in the civil case was largely circumstantial, with Olenn and expert witnesses theorizing that Swain had wrestled her from behind and shut off her air supply. The chief medical examiner of Dade County, Fla., testified that Tyre's death, in his opinion, was a "homicidal drowning."

One witness said Swain instructed him to get rid of the scuba equipment. Thwaites testified that he began performing mouth-to-mouth resuscitation on Tyre and that Swain briefly tried CPR. But he said Swain curtailed the efforts, quoting him as saying, "Shelley's gone. It's over."

Denner challenged that account and said Swain's behavior was "absolutely consistent with that of an innocent person who was incredibly traumatized by the incident."

Olenn also laid out a possible motive, arguing that Swain wanted his wife dead to pursue an affair with another woman — who said in a videotaped deposition played at trial that she was not interested in a relationship with Swain while he was married but became involved with him after Tyre's death.

Olenn said Swain knew he would benefit financially from Tyre's death under their prenuptial agreement.

"It's a grand story but it's just not true," Swain has said of the accusations against him.

Swain told jurors in the civil trial that his relationship with the other woman was non-sexual, and that he was working on his marriage when Tyre died. He also said he was not capable of such violence, especially while vacationing with friends and their child.

Swain's friends and family insist he's innocent and have raised money for his defense. They say his even-keeled temperament and relative nonchalance at his civil case may have masked the heartache he felt at Tyre's death.

"Let's put it this way: I wouldn't have had him certify my 13-year-old son if I thought he was guilty," said John Stanford, a fellow diver and longtime Swain friend.

Federal agents arrested Swain at his dive shop in November 2007 and he was extradited to Tortola.

"He's relieved to have everything laid out and to look at the actual facts," said Jennifer Swain-Bloom, his daughter from a previous marriage. "The only thing we do know is that my father had nothing to do with it because he was nowhere near her."

The British court trial before a 9-person jury is scheduled to start Wednesday. The criminal charges carry a higher burden of proof than the earlier civil case. Swain faces life in prison if convicted.

"We've lost a daughter, no amount of whatever happens can compensate for losing your daughter," said Richard Tyre. "We just hope justice is performed."