Lewis Bennett and his wife Isabella Hellman had just welcomed a new daughter when they set sail last April with the intention of sailing from St. Maarten to Florida on a catamaran named "Surf Into Summer."
Bennett was the captain, a skilled swimmer and sailor. His wife was a weak swimmer with less sailing experience, according to court papers. Unlike her husband, she wasn't trained on how to handle emergencies, prosecutors say.
But two weeks into the trip, there was an emergency after they left Cuba. Bennett reported his wife missing in a distress call to the Coast Guard, who rescued him from a life raft about 30 miles west of Cay Sal, Bahamas, not far from Cuba in May 2017. Hellman's body was never found.
On Monday, the 41-year-old Bennett, who is a dual citizen of Australia and the United Kingdom, pleaded guilty to involuntary manslaughter in the death of his wife. The plea deal was struck after prosecutors originally sought a second-degree murder charge against Bennett, who was set to go to trial in December.
Bennett's attorney, Edward Downey, declined to comment on Monday.
Hellman's death resulted in part from her husband's "gross negligence, amounting to wanton and reckless disregard for human life," prosecutors said.
He did not require that his wife wear a life vest or harness despite her inexperience, nor did he deploy flares or turn the boat around to search for her when he couldn't find the 41-year-old real estate agent from Delray Beach, Florida, prosecutors said.
"Lewis Bennett will now be held accountable for his wife's death while on the high seas," Tom Jones, acting Special Agent in Charge of the FBI's Miami office said in a news release.
Bennett 'did not deploy flares,' prosecutors say
Early on May 15, 2017, a loud noise woke Bennett, who had asked his wife to take over the night watch, prosecutors said. Bennett noticed the sails and rigging were loose, and saw his wife wasn't at the controls, prosecutors said.
Bennett "could not recall whether" he called out his wife's name, prosecutors said.
"Although Mr. Bennett threw a horseshoe life ring overboard, he did not deploy flares to illuminate the area to look for his wife or to signal his position, nor did he turn the catamaran around to look for her," prosecutors said.
Neither did Bennett immediately activate a personal locator beacon or use a satellite phone to signal or call for help for Hellman, prosecutors said.
He tossed several items in his life raft, including a suitcase, two duffel bags, water, food and silver coins, and then abandoned the catamaran, prosecutors said. Bennett estimated that about 45 minutes to an hour had elapsed from the time he woke up until he abandoned the catamaran, prosecutors said.
Bennett made mayday calls with the catamaran's radio, but they were unsuccessful, prosecutors said.
Aboard the life raft, he used a satellite phone and activated a small battery-powered transmitting device to call for help and report his wife missing, prosecutors said.
Bennett also didn't discharge flares during the hours he lay waiting for the Coast Guard to rescue him, prosecutors said.
"Although he initially attempted to paddle the life raft to look for his wife, the life raft was hard to control, and he was scared to lean out to use the paddle, so abandoned his efforts," prosecutors said.
The Coast Guard searched for Hellman for three days before suspending the search.
Bennett told authorities at the time that the boat hit something while he was asleep, and the vessel began taking on water.
In February, authorities charged Bennett with second-degree murder. An FBI agent wrote in an affidavit then he believed Bennett intentionally scuttled the boat.
Photographs and video of the capsized vessel appeared to show that a small part of each hull -- the part of the ship that goes underwater -- was breached, and the damage to the hull came from the inside of the vessel, the affidavit said.
A Naval expert concluded that "the holes in the hull under the forward hatches are unexplainable as structural failures due to the working of the vessel or as a result of a collision ... I cannot think of any items that would accidentally cause similar holes in both hulls at roughly the same time," according to the affidavit.
When asked by the FBI what he did to find Hellman, Bennett "indicated he did not do anything" like call out for her or use flares to illuminate the water, the affidavit said. Bennett told other agencies he yelled out for his wife and threw out a buoy, according to the affidavit.
The 'pain is unbearable,' victim's family says
Bennett was sentenced in February to seven months in federal prison for transporting stolen gold and silver coins on the same trip. He faces up to eight years after his plea of involuntary manslaughter when he is sentenced on January 10.
In a family statement, obtained by CNN affiliate WPTV, Hellman family attorney Joel Weissman said his clients' "hearts are broken."
"Although they already knew, they now have confirmation, that their beloved daughter and sister, Isabella, was never coming back to us, we now have confirmation that she was taken from us by her husband, Lewis Bennett. The pain he has caused them is unbearable and never goes away," the statement said.
CNN's Steve Almasy, Chris Boyette and Tony Marco contributed to this report.