HARTFORD, Conn. — It was a crime that stunned a quiet suburb and stumped investigators: an 87-year-old real estate developer killed in his home, shot three times with a rifle.

Nearly three years later, the unsolved case has received new attention with the revelation the victim’s grandson Nathan Carman, who was rescued Sunday after a week in a raft on the Atlantic Ocean, had been a suspect in the killing. Carman’s mother, Linda Carman, was not found with him and is presumed to have drowned after their boat sank during a mother-and-son fishing trip that is now under investigation by federal, state and local authorities.

Nathan Carman, of Vernon, Vermont, has denied having anything to do with his grandfather’s slaying. His father also said Nathan Carman could not have been involved, and his mother had told her lawyer that he was innocent.

“She was convinced he had nothing to do with it,” Linda Carman’s lawyer, Gerald Klein, said Thursday.

Police, however, were so confident they had enough evidence against Nathan Carman, 22, that they applied for an arrest warrant charging him with the murder of John Chakalos at his home in Windsor, Connecticut. A prosecutor returned the warrant unsigned to investigators with a request for more information. No arrest has been made in the case.

A search warrant said that Carman was the last person known to have seen Chakalos alive, that Carman had bought a rifle consistent with the one used in the crime and that he discarded his computer hard drive and GPS unit used around the time of the shooting. The warrant also said investigators learned Carman was “capable of violence” based on past behavior, including when he held another child hostage with a knife.

The state’s attorney in Hartford, Gail Hardy, did not respond to questions about why the request for an arrest warrant was sent back. The state Division of Criminal Justice said it doesn’t comment on pending investigations.

The shooting of Chakalos left friends and neighbors puzzled over who would attack a man known for having a kind word for all he met. Chakalos also kept a home in Chesterfield, New Hampshire, that was known for its massive holiday lights display. He left an estate worth more than $42 million to his four adult daughters, including Linda Carman.

Nathan Carman had dinner with his grandfather the night of the killing. Police said the grandfather was slain between 10 p.m. on Dec. 19 and 8 a.m. the next day.

Linda Carman told police she was supposed to meet her son at 3 a.m. on Dec. 20 in Glastonbury to go on a fishing trip. When he didn’t show up, she went back home to Middletown. At about 4 a.m., Nathan Carman called his mother on his cellphone and said he was in Glastonbury, according to the warrant.

In an interview Wednesday with The Associated Press, Nathan Carman said he’s not generally a punctual person.

“I was late in meeting my mom as I frequently was,” he said. “I’m not always the person who is on time.”

He denied involvement in his grandfather’s killing, saying his grandfather was the closest person in the world to him. He said suspicions about his account of the sinking of his boat are compounding his grief over the apparent drowning of his mother.

Linda Carman was initially under police scrutiny for her father’s killing because she had been charged in 2011 with assaulting him during an argument at a Hartford psychiatric hospital, where Nathan Carman was being treated, Klein said. The family members were fighting over Nathan Carman’s care, and there was a dispute about money, Klein said. The assault charge against Linda Carman later was dropped.

On Sept. 17, mother and son set off from a marina in South Kingstown, Rhode Island, authorities said. Nathan Carman said their boat sank in a matter of minutes the next day after he heard a “funny noise” in the engine compartment and saw water pouring in.

Associated Press writers Denise Lavoie in Boston and Michael Melia in Hartford contributed to this report.