Nathan Carman survives seven days at sea after his boat capsizes, but his mother remains missing.

The dramatic radio call from sole survivor Nathan Carman to the Coast Guard has been released.

He and his mother, Linda Carman, plunged into the cold Atlantic Ocean off the eastern seaboard during an overnight fishing trip. They were reported missing on September 18.

Nathan, 22, claims water overtook his 31-foot aluminum boat named Chicken Pox. He says he grabbed the only life raft onboard. Nathan claims he clung to the life raft for seven days until a passing freighter rescued him on Sept. 25.

But before he could dry off, a cloud of suspicion had fallen over Nathan. Was he fishing for murder?

The mystery begins at a marina in South Kingstown, Rhode Island.

Nathan and his mom are headed toward Block Island. Friends tell Crime Watch Daily Hartford, Connecticut affiliate WTIC this was a mother-son bonding trip.

When they didn't return, the Coast Guard launches a massive search. They scour some 60,000 square miles of open ocean, stretching from Long Island up to Cape Cod.

Linda Carman, 54, was nowhere to be found.

But then an unexpected twist: Questions surface about Nathan. One of them asking, Was he trying to dump his mother at sea?

Today Nathan is the target of a multiagency investigation by federal, state and local authorities.

Police execute a search warrant at his house in Vernon, Vermont. They seize a cable modem, a GPS SIM card and a letter he wrote.

According to the search warrant, Nathan took his mother "... Fishing farther off-shore" than planned, and made repairs "... Which could have potentially rendered his boat unsafe for operation."

And in Connecticut, cops searched Linda's home for clues, taking out bags and boxes of possible evidence.

Nathan has been diagnosed with Asperger's Syndrome. People with Asperger's have difficulty in social interactions.

This isn't the first time Nathan has been in the news. Back in 2011 he went missing after his horse died. He was found a few days later in Virginia.

Then three years ago Nathan's grandfather, John Chakalos, was murdered in his Windsor, Connecticut home. Chakalos was a wealthy real estate developer worth a reported $42 million.

There are reports today that the family had clashed over money and that Linda is an heir to the estate.

Linda's attorney tells a Boston newspaper she was initially considered a suspect in her father's killing. That's because she allegedly assaulted him in a hospital ward two years earlier. That charge was eventually dismissed. Cops still consider Nathan a person of interest in the killing. They say Nathan was the last person to see his grandfather alive.

Court documents say police found a .308-caliber rifle in Nathan's home consistent with the caliber of bullet that killed Chakalos. The documents reveal Nathan's allegedly violent past, saying the family feared him so much they "hired armed private security to protect them in their homes."

According to the documents neighbors called him "Murder Boy," and a "time bomb waiting to go off."

Police sent an arrest warrant to the prosecutor, but it was returned unsigned with a request for more information. Nathan was never charged.

Nathan's father tells Crime Watch Daily Boston affiliate WBZ his son is not a killer.

Nathan insists he had nothing to do with his grandfather's murder and says he did not harm his mother.

Meanwhile friends and neighbors of Linda are holding out hope that she'll be found alive.