The man charged with killing his mother at sea during a 2016 fishing trip off the coast of New England has died awaiting trial, federal authorities in Vermont said Thursday.

Nathan Carman, 29, of Vernon, Vermont, was scheduled to face trial in October in what prosecutors said was a scheme to inherit millions of dollars. He had pleaded not guilty last year to fraud and first-degree murder in the death of his mother, Linda Carman of Middletown, Connecticut.

The cause of Nathan Carman's death was not immediately clear.

One of his lawyers, Martin Minnella, said he was told about Carman’s death Thursday by the U.S. Marshals Service.

“We had spoken to him yesterday. He was in good spirits,” Minnella said. “We were meeting with some experts today over Zoom at 12 o’çlock. We were prepared to start picking a jury on Oct. 10 and we were confident we were going to win. It’s just a tragedy, a tragedy.”

The U.S. Marshal informed prosecutors that Carman had died “on or about” Thursday, said Vermont U.S. attorney’s office spokesperson Fabienne Boisvert-DeFazio in a statement. Carman was in U.S. Marshals custody, “as is the case for all pretrial defendants who are detained.”

In September 2016, Carman arranged a fishing trip with his mother, during which prosecutors say he planned to kill her and report that his boat sank and his mother disappeared in the accident.

He was found floating in an inflatable raft eight days after leaving a Rhode Island marina with his mother, who was never found. Prosecutors allege he altered the boat to make it more likely to sink. Carman denied that allegation.

The eight-count indictment also says Carman shot and killed his wealthy grandfather John Chakalos at the man's Connecticut home in 2013, as part of a scheme to obtain money and property from his grandfather’s estate. But the indictment does not charge Carman with murder in his death.

Minnella and fellow attorney David Sullivan, both from Connecticut, where Carman grew up, had criticized the indictment, including allegations Carman killed his grandfather, saying Carman was never charged with that crime.

“The whole situation would have come out in court,” Minnella said Thursday. “This young man would have been vindicated.”

Assistant U.S. Attorney Paul Van de Graaf said in court in February that Chakalos’ “murder” was part of the fraud charge.

“As a central part of the scheme, Nathan Carman murdered John Chakalos and Linda Carman,” the indictment read.

Prosecutors say the inheritance scheme spanned nearly a decade and began with Carman buying a rifle in New Hampshire that he used to shoot Chakalos while he slept on Dec. 20, 2013. Carman then discarded his own computer hard drive and the GPS unit that had been in his truck, prosecutors said.

Police have said Carman was the last person to see his grandfather alive and owned a semi-automatic rifle similar to the one used to kill Chakalos — but the firearm disappeared.

After Chakalos’ death, Carman received $550,000 from two bank accounts that his grandfather had set up and that he was the beneficiary of when Chakalos died. He moved from an apartment in Bloomfield, Connecticut, to Vernon, Vermont, in 2014.

He was unemployed much of the time and by the fall of 2016 was low on funds, prosecutors said, which is when he arranged the fishing trip with his mother.

Chakalos’ three surviving daughters sued Carman in New Hampshire probate court, seeking to bar him from receiving any money from Chakalos’ estate. A judge dismissed the case in 2019, saying Chakalos was not a New Hampshire resident. The probate case was refiled in Connecticut and is still pending.

Carman’s three aunts — his late mother’s sisters — said in a statement Thursday that they were “deeply saddened” to hear about Carman’s death.

“While we process this shocking news and its impact on the tragic events surrounding the last several years we ask for your understanding and respect relative to our privacy,” they said in a statement provided by their lawyer, William Michael.

In 2014, police in Windsor, Connecticut, drafted an arrest warrant charging Carman with murder in his grandfather’s death, but a state prosecutor declined to sign it and requested more information. No criminal charges were brought until the federal indictment.