A man found floating on a raft off the shore of Rhode Island in 2016 after his boat sank was charged on Tuesday (local time) with murdering his mother at sea to inherit the family's wealth.

According to the eight-count indictment filed in federal court in Burlington, Vermont, Nathan Carman shot and killed his grandpa, John Chakalos, at his house in Windsor, Connecticut, in 2013 as part of a scheme to defraud insurance companies; however, he was not charged with that murder.

Carman was discovered on an inflatable raft eight days after fishing with his mother, Linda Carman, who was never located.

Carman, age 28, was taken into custody on Tuesday. Wednesday, he is scheduled to appear in federal court in Rutland, Vermont. His attorney did not respond to a phone requesting comment.

The attorney for Carman's mother's sisters, William Michael, stated that the family had no immediate response on Tuesday.

A federal judge in Rhode Island determined in 2019 that Carman contributed to the 2016 sinking of the vessel in which his mother perished at sea.

US District Judge John McConnell delivered a written ruling in favor of an insurance carrier that had refused to compensate Carman $85,000 (NZ$135,100) for the loss of his 9-meter fishing vessel, The Chicken Pox.

Carman denies any involvement in making the boat purposefully unseaworthy. He told the Coast Guard that when the boat soon filled with water, he swam to the life raft and yelled for his mother, but he never saw her again.

The judge determined, among other things, that Carman conducted incorrect boat repairs before his fishing expedition with his mother. According to the testimony of witnesses, he removed two stabilizing trim tabs from the vessel's stern at the waterline, causing holes that he attempted to fix with an epoxy stick.

The crew of a freighter discovered him drifting in the raft off the shore of Martha's Vineyard, a Massachusetts island, eight days after the boat was reported lost.

Some of Carman's family suspected him murdering his mother and grandfather to gain $7 million (NZ$11.13 million).

Nathan Carman was identified as a "person of interest" in the 2013 murder of Chakalos, who was shot in the head at his house. No criminal charges were made against him in relation to the death of his grandfather.