Police are investigating the circumstances of a mother-son fishing trip that ended with the rescue of the young man who was lost at sea for a week and the disappearance of his mother, who is presumed dead.

A freighter found Nathan Carman, 22, alive on a raft on Sunday, a week after he and his mother, 54-year-old Linda Carman, went fishing off the coast of Rhode Island. 

The U.S. Coast Guard has said that they will not reopen a search for Linda Carman. 

Nathan Carman was brought to the Coast Guard's base in Boston Tuesday morning, where he was reunited with his father, according to the Coast Guard.

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Carman told the Coast Guard that their boat made a funny noise. When it began taking on water, he moved to the life raft but could not find his mother.

"I was whistling and calling and looking around, and I didn't see her," he said.

Carman was able to return to his Vernon, Vermont, home that night. Local police issued a search warrant for that home and seized several items, including a modem, SIM card and letter he wrote, WBZ reported.

According to court records obtained by the Hartford Courant, Carman was a suspect in the 2013 fatal shooting of his grandfather. He was never charged because the arrest warrant was returned with a "request for further information," according to the Courant. 

Carman was the last person to see his grandfather alive on Dec. 20, 2013. He had dinner with him in Windsor that night and the 87-year-old man was found dead the next morning, having been shot three times, The Associated Press reported.

Carman has Asperger's syndrome, according to WBZ, and disappeared from his home five years ago when he was upset over the death of his horse. He was found four days later in Virginia.

An investigation by Rhode Island police revealed that Carman's boat was in need of mechanical repair and that he had been doing repairs on his own, "which could have potentially rendered the boat unsafe for operation," South Kingstown Det. Lt. Alfred Bucco III wrote in an affidavit, according to the Courant. 

As of Wednesday morning, Carman had not been charged with anything.