BOSTON — A 22-year-old man rescued in the Atlantic after floating on a life raft for a week had been a suspect in the 2013 slaying of his grandfather, deepening the mystery surrounding his ordeal and the apparent death of his mother at sea.

According to a search warrant for Nathan Carman’s apartment obtained by the Hartford Courant, Carman was the last person known to see his maternal grandfather, John Chakalos, alive on Dec. 20, 2013, because he had dinner with him at his home in Windsor, Connecticut. The 87-year-old Chakalos, a real estate developer, was found dead the next morning. He had been shot three times.

The Courant reported Tuesday that Windsor police submitted an arrest warrant for Carman to a prosecutor, but it was returned unsigned with a request for more information. Carman was not charged.

A will shows Chakalos left an estate worth more than $42 million to his four adult daughters.

Carman and his mother, Linda Carman, 54, of Middletown, Connecticut, left Rhode Island on a fishing trip on Sept. 17. Nathan Carman was rescued in a life raft off the Massachusetts coast on Sunday. His mother remains missing and is presumed dead.