Nathan Carman, shown at federal court in 2019 in Providence, R.I., has pleaded not guilty in his mother’s death. Steven Senne/Associated Press

RUTLAND, Vt. — A 28-year-old man who was rescued from a raft off the coast of New England in 2016 after his boat sank pleaded not guilty Wednesday to charges he killed his mother at sea to inherit the family’s estate.

Nathan Carman was arraigned in federal court in Rutland on multiple fraud charges and a first-degree murder charge in the death of Linda Carman. He shouted “not guilty” in the direction of reporters who had asked him on his way into the courthouse whether he killed his mother.

Authorities allege in the indictment unsealed Tuesday that Carman also killed his grandfather, John Chakalos, at his home in Windsor, Connecticut, in 2013 as part of a scheme to obtain money and property from his grandfather’s estate, but he was not charged with that killing.

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

Carman was found in an inflatable raft eight days after leaving a Rhode Island marina to go fishing with his mother, who was never found. Prosecutors allege Carman altered the boat to make it more likely to sink that day. He has denied doing anything to intentionally make the boat unseaworthy.

Carman, who was arrested Tuesday, faces life in prison if convicted of killing Linda Carman, his mother. His attorney did not comment after the arraignment.

Federal prosecutors said in a court document filed Wednesday he should remain detained because he poses a flight risk and is a danger to the community. They wrote that Carman was treated for mental health issues from when he was a small child until he was 17 years old and has avoided any treatment since then.

“For an individual who would kill his own family members, nothing is off the table,” prosecutors wrote. A hearing is scheduled for Monday.

Federal agents execute a search warrant at Nathan Carman’s residence in Vernon, Vt., after he was arrested and charged with the 2016 murder of his mother on Tuesday. Kristopher Radder/The Brattleboro Reformer via Associated Press

Prosecutors allege the inheritance scheme that has spanned nearly a decade began with Carman buying a rifle in New Hampshire that he used to shoot Chakalos on Dec. 20, 2013, while he slept. He then discarded his 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.

In September 2016, Carman arranged to go on a fishing trip with his mother on his boat named the “Chicken Pox.”

“Nathan Carman planned to kill his mother on the trip,” the indictment reads. “He also planned how he would report the sinking of the ‘Chicken Pox’ and his mother’s disappearance at sea as accidents.”

Before the trip, Carman altered the boat by removing two forward bulkheads and trim tabs from the transom of the hull, the indictment states.

“After leaving the marina, Nathan Carman killed his mother, Linda Carman, and eventually sank the Chicken Pox,” it states.

In 2019, a federal judge in Rhode Island decided that Carman contributed to the sinking of the boat. U.S. District Judge John McConnell issued a written decision in favor of an insurance company that had refused to pay an $85,000 claim to Carman for the loss of his 31-foot fishing boat.

Carmen denied the allegations, telling the Coast Guard that when the boat filled quickly with water, he swam to the life raft and called for his mother but never saw her again.

He was found floating in the raft off the coast of Martha’s Vineyard, a Massachusetts island, by the crew of a freighter eight days after the boat was reported missing.

Chakalos, who was a real estate developer, left behind an estate that was worth nearly $29 million, which was to be divided among his four daughters. Carman is in line to get about $7 million of the estate, as his mother’s only heir.

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, where it remains pending.

William Michael, an attorney for Carman’s mother’s sisters, said Tuesday the family had no immediate comment.

AP reporters Kathy McCormack in Concord, New Hampshire, Lisa Rathke in Montpelier, Vermont, and Dave Collins in Hartford, Connecticut, contributed to this report.