BOSTON (WPRI) — A man who spent more than a week adrift in a life raft returned to shore Tuesday morning while his mother remains missing.

The Windham County Sheriff’s office confirmed Tuesday they searched Nathan Carman’s home in Vernon, Vermont, on behalf of the South Kingstown Police Department, who’s heading up the investigation.

South Kingstown Police Chief Vince Vespia confirmed for Target 12 they are conducting an investigation to determine if a crime had been committed.

“Some of the aspects of the report of their [disappearance] is confusing to us, and we want to clarify that,” Vespia said. “We have also been in touch with Connecticut authorities who are conducting a separate investigation into Carman’s grandfather’s death; we’re working in conjunction with them.”

Carman’s grandfather was murdered in December 2013. The Hartford Courant is reporting Carman was a suspect in his grandfather’s death.

“We’re working in conjunction with them,” Vespia said. “Now we are working in connection with Vermont authorities to see if there is a common denominator linking the two cases.”

Vespia said he is sending detectives to Connecticut on Wednesday to work with authorities there.

“It’s complex and going to require a lot of field work and we are prepared to do that,” he said.

Vespia declined to specify what aspects of the pairs disappearance prompted them to launch an investigation.

A search warrant to search Carman’s home – obtained by CBS affiliate WCAX in Vermont – stated police are trying to determine where exactly Carman was planning on taking his mother fishing.

“The investigation revealed that Nathan’s boat was in need of mechanical repair and that Nathan had been conducting a portion of these repairs upon his own volition which could have potentially rendered his boat unsafe for operation,” Detective Alfred Bucco wrote in the affidavit for the search warrant. “The investigation has also revealed that Nathan had intended to go fishing farther off-shore in a different location than what were his mother’s intentions and understanding.”

He goes on to say police believe “that evidence revealing Nathan’s destination on the fishing trip will be recovered in Nathan’s residence.”

Carman, 22, arrived at about 9:45 a.m. at the Coast Guard base in Boston. Wearing a white jumpsuit and rubber boots, he was quickly whisked away in a black government vehicle.

A passing freighter found Carman Sunday on a four-person life raft about 100 nautical miles south of Martha’s Vineyard.

Carman and his mother, Linda, 54, set out from Ram’s Point Marina in Point Judith in a fishing boat on Saturday, Sept. 17. The 32-foot aluminum center console boat took on water in the vicinity of Block Canyon off New York and sank, but the reason was not known, according to the Coast Guard.

In his initial interview with the Coast Guard, Nathan said he tried to find his mother after their boat sank, but was unable to locate her.

Nathan will now participate in a survivor debriefing and a closed-door interview with investigators. He’s also set to meet with his family and a lawyer.

Coast Guard Petty Officer 3rd Class Nicole Groll said there are no plans to reopen the search to find Linda; they are beyond “the survivability window,” she said. There are also no plans to try and recover the boat from the deep sea.

This isn’t the first time tragedy has hit the family. In 2013, Nathan Carman’s grandfather was shot in the head and killed in Connecticut. There were no arrests made. Two years prior to that in 2011, Nathan went missing after becoming distraught over the death of his horse. He was found in Sussex County, Virginia.