SOUTH KINGSTOWN, R.I. (CBS) — The mysterious case of the missing Connecticut woman whose son was rescued off the coast of Martha’s Vineyard this week, is now the subject of a federal investigation spanning several New England States.

Police in South Kingstown, Rhode Island have been investigating whether Nathan Carman should face charges for allegedly taking his mother, Linda Carman, to a risky fishing spot in a boat that was not safe. They say they’re now joining forces with federal, state, and local law enforcement from Connecticut, Rhode Island, and Vermont.

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Nathan Carman arrives at the Coast Guard base in Boston, Sept. 27, 2016. (WBZ-TV)

Nathan Carman arrives at the Coast Guard base in Boston, Sept. 27, 2016. (WBZ-TV)

This week, a freighter rescued him from a life raft he said he’d been in for more than a week after his boat capsized. Carman, who has Asperger’s Syndrome, said his mother disappeared during the ordeal.

“I didn’t know if she had been dragged down with the ship,” he told Good Morning America, “because neither of us had been wearing life vests.”

A search warrant police used to search Carman’s Vernon, Vermont home, says he told witnesses he was headed to a fishing spot called “the canyons”, a place his mother had refused to go to in the past. The warrant also quotes witnesses who said his boat had mechanical problems that he had tried to repair himself. The warrant says he removed “trim tabs” and filled the holes with a marine adhesive.

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A boat maintenance worker near the Rhode Island marina where he kept his boat tells WBZ removing trim tabs can be dangerous.

“If it was a bow-heavy boat and it didn’t have trim tabs, I could see how it would go down,” said Austin Glazier. He also described the canyons as unprotected, far from shore, and very deep.

Nathan Carman has also been at the center of an investigation into his grandfather’s homicide, which is still unsolved. John Chakalos was found shot to death in his Windsor, Connecticut home nearly three years ago. Nathan Carman was the last known person to see him alive.

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Carman told Good Morning America, “I had absolutely nothing to do with my grandfather’s death.”