The man who was on a boat his mother that sank off the coast of Rhode Island may have tampered with the vessel before setting sail in an attempt to kill his mother.

According to the Boston Globe, Nathan Carman, 23, is accused of enlarging holes in a boat before taking his mother, Linda Carman, on a fishing trip in 2016 from which she never returned.

The Coast Guard rescued Nathan a week later over a 100 miles from Martha’s Vineyard, as he was floating on a life raft, but his mother, an heir to a $44 million fortune, was never found and is presumed dead.

From the start, investigators reportedly suspected Nathan may have engineered the sinking by tampering with the boat, and taking his mother further out in the water than she had planned or expected.

The Boston Globe reports that the boat’s insurer, National Liability and Fire Insurance Co., asked a court to deny any insurance claim on the boat following an investigation that revealed Nathan compromised it before the accident.

In removing his boat’s trim tabs hours before departing on its final voyage, Carman not only failed to properly seal four thruhull holes he thereby opened at the transom’s waterline, but two recent depositions establish Carman enlarged those four holes,” the insurer reportedly wrote in the request.

This is not the first time Carmen has been eyed for a murder of a family member: He was reportedly named a person of interest in the 2014 shooting death of his wealthy grandfather, John Chakalos.

According to warrants obtained by CBS News, Carman was the last person to see his grandfather alive before the 87-year-old man was found shot to death in his Windsor, Connecticut, home. Nathan reportedly purchased a gun that was the same caliber as the weapon that killed his grandfather, a multimillionaire developer, and declined to let police know this during questioning. He also declined to take a polygraph test.

Chakalos left his $44 million estate to his children, including Linda Carman.

Nathan has reportedly denied involvement in both his grandfather’s and mother’s death, and has not yet been charged in either case.

[Feature image: Associated Press/Nathan Carman]