People alive. Tonight, a 20 20 investigation, and the only reporter to have spoken to him. A lot of people would say his speech patterns are different because he is different, he has as aspergers. Now, with an unsolved murder in the familys past and a new strike just nathan just this week and its not good news for nathan. They want to explore whether or not you sank the boat on purpose. Were done here this evening. Good evening. Im elizabeth vargas. And im david muir. As we come on the air, breaking news, this is a story out of to movies. Rescued at sea after floating for a week. But a major new twist. An Insurance Company is saying the boat sank due to intentional acts. Let us know what you think on facebook and twitter. How linzie janis got this exclusive is a story all in its own. Reporter my name is devin. I work the overnight shift at abc news. On the night of september 26th, i saw that one of the affiliate reporters had tweeted about someone who had been rescued at sea. I sent it around, but, you know, of course we didnt have too many of the details besides that he had been found. He was found in a life raft, with a life jacket on. He was reported to be in good condition. Reporter they sent linzie janis. Linzie janis. Linzie janis has that story for us. Reporter the freighter is due to arrive in boston. When i first heard about the Nathan Carmen story, it looked like an inspiring story of survival. The son rescued off martha`s vineyard. Reporter nathan had gone out on this fishing boat with his 54yearold mother linda and never returned. The coast guard combed hundreds of miles of ocean in vain and theyd just given up hope when the call came in. A young man found alone floating on a life raft. Found alive in good condition. Reporter the stunning discovery made in the open ocean by this chinese freighter carrying scrap metal, about 100 miles south of ram point marina in rhode island, where hed set sail. Theyll get the chance to speak with Nathan Carman tuesday night. Nathan, this is u. S. Coast guard boston. I need to understand what happened. Reporter yeah, we all do. But so far, the only explanation, this short radio call from the coast guard to nathan aboard that freighter. Mom and i, two people. Myself and my mom were fishing at block canyon. And there was a funny noise in the engine compartment. When i saw the life raft, i did not see my mom. Have you found her . No, we have not been able to find her yet. Reporter the next day, nathan arrives in boston. The questions waiting for him at the dock. The most important question is, how did you survive and not your mother . Reporter when we first see him, he shows little emotion. His 63 frame awkwardly appareled in the white crew suit he was given after his rescue. That night, nathan returns to his home in Rural Vermont and makes his first public statement. I would just like to thank the public for their prayers and for their concern for both my mother and for myself. Emotionally, ive been through a huge amount and my request is just to be allowed to mourn naturally. Reporter it seems thats all he has to say. But then nathan decides to grant us an exclusive interview. He instructs us to meet him on this bench. He seems anxious, traumatized. Im not sure how best to say this. Reporter worried he wont look or sound good on camera. Oh, lord, may you help us to reporter he even prays about it. Help me to accurately and effectively express what i have been through. Reporter theres a reason nathan doesnt speak in the tongues of angels. He has been diagnosed with aspergers syndrome, which is on the autism spectrum, associated with social awkwardness and flat, measured speech patterns. Lets begin, if we could, with the fishing trip. Our conversation will last into the night but it ends up a fragmented account with plenty of blank spaces. Im not going to go into that now. Im not going to answer that. Im not going to go there. Reporter but nathan is able to provide more details about that ordeal at sea. My mom and i fished very frequently together. Thats the primary thing we did to spend time with one another. We fished probably every other week. Reporter despite his humble appearance, it turns out nathan is actually from a wealthy new england family. The first of many surprises. His mom linda, a nurse who worked with autism patients, didnt even like to eat fish. But she loved catching them with nathan. In this facebook posting, she said, there was no better way to connect. Nathan had purchased this nathan had purchased this 31foot fishing boat, named the chicken pox, after seeing it advertised online. He says that on september 17th, he and his mom set out for that fateful trip just before midnight. These fishing trips, you would often leave, what, at night or in the early hours of the morning . Thats correct. We met at the marina in rhode island, got all of our gear on board, pushed off from the dock. Reporter nathan wanted that night to be different. He says that instead of the usual trip of about 20 miles to block island for striped bass, he decided to go deep sea tuna fishing, to that area called block canyon. Thats much farther offshore. Thats offshore fishing. Reporter it takes all night to get there. The sea bed here drops from a few hundred feet below the surface to 1,000 feet or deeper. A perfect spot for those giant tuna they were after. I have experience boating. I have experience fishing. I did not have experience offshore fishing. Reporter but nathan was comfortable making the trip because, he says, the seas were calm after a smooth cruise through the night. We arrived just as the sun was rising. Reporter nathan says the new day was perfect. They set their lines and fish for tuna, all by themselves. They have life vests onboard, but werent wearing them. Hours passed. It was midday when he says the trouble started. So what happened . What went wrong . I heard a noise. Reporter a funny noise coming from the engine. The engine sounded different. I looked in the hatch where the engine was, i observed there was water. Quite a bit of water. The belt on the engine was picking up water and kind of spinning it. Reporter what did you think . I knew there was a serious problem. But i didnt think we were sinking. I thought i was going to diagnose the problem and that we were going to go back to shore. Reporter he says he closed the hatch and shut off the engine. He says he told his mother to gather the fishing lines in the rear while he says he brought the ditch bags full of safety gear up to the front. But he says to his shock, in no time the boat was under water. I was walking on the deck. It was there. And then it wasnt. Reporter any sign of your mother at this point . No. Not at that point. Reporter he claims he was totally disoriented. Doesnt remember hearing his mother or seeing her. The life raft was designed to inflate automatically. Nathan says he swam to it. I got onboard the life raft and was looking around and i was calling out to my mom. I did not see or hear my mom. I was blowing the whistle with three loud, short bursts, which is a distress signal. Reporter so if she had been on the surface of the water you feel like you wouldve been able to see her . I assumed that if she had been on the surface and conscious that she wouldve been calling out to me and i wouldve been able to find her. But i didnt know why that hadnt happened. Reporter now, by his account, he was all alone in a kind of floating tent. A tiny speck of orange in a vast grey sea. As that night fell, he was drifting in the darkness. Like tom hanks in castaway, nathan says he spent days alone out in the open water until just like the movie, the freighter that saved nathan, aptly named the orient lucky, was docked when we intercepted it later that week. Theyd recorded this remarkable footage of the rescue. Look here, that little figure is nathan, clinging to a life preserver, clinging to life, then jumping into the churning seas. As the ship struggles to stay close enough to grab him. We could see he was very tired. Exhausted. He rested for a while clinging on to the ladder. Our crew helped for him to get onboard our ship. I was no longer lost and thats when i allowed myself to feel relief. Reporter what was going through your mind . Im safe. Reporter its a compelling, heartstringtugging story of loss and survival. That i love my mother, present tense, i love my mother. Reporter but is it also something more . Police want to know, what role, if any, Nathan Carmen played in his mothers disappearance. Wait a second. Was this just an accident . Reporter is his story really the whole story . As more details emerge, the portrait of the young fisherman takes on a darker hue. It paints a very troubling picture as to what was nathans intent. Ople in here. Their training is developed by the same company who designed, engineered, and built the cars. Theyve got the parts, tools and knowhow to help keep your ford running strong. 35,000 specialists all across america. No one knows your ford better than ford. And ford service. Right now, get the works a Synthetic Blend Oil change tire rotation, Brake Inspection and more for 29. 95 or less. Sitting in the sunshine by the trees pretty little love birds sing to me they dont got a care, just a melody, yeah, yeah burts bees lipstick. Vibrant color youll love. 8hour moisture that loves you back. pop campbells tomato soup and grilled cheese. more popping go together like being late and being grounded. Made for real, real life. ™ your true self is never lost. 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So why are people so suspicious about what exactly happened to nathans mother linda . Now officials are investigating just how the 31foot boat sank. Reporter that suspicion deepens as we learn that the motherson relationship could be as choppy as the north atlantic. Well, i think anyone who has a child that has autism or aspergers, its difficult. There were conflicts on occasion, but he considered her his best friend. Reporter in addition to any personal friction, investigators see a possible financial incentive for foul play. Is nathan due to get a huge windfall . Is he due to get all of his mothers money . Thats my understanding. Reporter millions of dollars . Yes. Think its around 7 to 8 million. Reporter thats why a phalanx of investigators local police, the coast guard, even the fbi are taking a hard look at signs of possible criminal activity on that doomed boat. And so are we. This is ram point marina in rhode island, where nathan and linda set sail that night in september. Welcome aboard. Come on in. Reporter captain Dave Mccormick runs irish jig charters and was out fishing the day nathan and his mother set out on that sevenhour trip to block canyon. Captain dave considers it highly unusual for a mother and son to fish alone for tuna. Those fish can weigh hundreds of pounds. Theres usually a crew of four, and its usually all experienced guys. Reporter usually a crew of four experienced fishermen. Usually. You know, to be smart about things. Reporter on top of that, captain dave says a 31foot boat like the chicken pox would be too small a vessel for even the most experienced fisherman. And remember, nathan had never done this before. First time youre taking your boat that far offshore . Thats correct. Reporter captain dave is also puzzled by nathans actions after he says he reached block canyon and realized the boat was taking on water. There was a functioning alert system onboard, but nathan never used it. How long does it take to activate or make a mayday call . Its just a matter of seconds. You just flip the switch, and its activated if its a manual type. Reporter the coast guard said there was no mayday call. Did you have a radio on the boat . I had a radio, and there was also an emergency positionindicating radio beacon. I didnt know that we were sinking. I knew that we had a problem, but i didnt know that we were sinking until we sank. If you look at nathans behavior, if you take all of those things collectively together, it paints a very troubling picture as to what was nathans intent and what actually did happen to his mother. Hello, this is Nathan Carman. Reporter and what to make of nathans seemingly odd behavior just listen to his call with the so i got to the life raft after i got my bearings, and i was whistling and calling and looking around and i didnt see her. Affect is as flat as pavement as he recounts the tragic loss of his mother, asking about her seemingly as an afterthought. When i saw the life raft, i did not see my mom. Reporter but wait before you judge. Psychologist dr. Rebecca sachs says people with aspergers often speak without emotion, and order their thoughts in a way w others might find unusual. Important piece of information is often really, really difficult. Theyll sort of give information in a linear fashion. Reporter so youre saying that its not necessarily unusual that he didnt lead with, my mother is missing . Correct. Reporter sachs also says people with aspergers affects how he interacts with others, and can lead to misunderstanding. Take what happened at this donald trump rally in New Hampshire, which nathan attended just weeks before his mothers disappearance. Nathan who told us hes a big trump supporter was removed from the rally after the man who took this photo reported him to security because he said he was uncomfortable with nathans demeanor. And now, watch this odd moment during our interview when nathan reveals his mother needed coaxing to go on that fishing trip at all. She was concerned about safety . Thats correct. It was not an argument. I was kind of pestering my mom. She had always been kind of skittish were stopping right here with that question. Reporter oh. Okay. Out of nowhere . Stopping right there. Reporter and its like, what happened . I sometimes talk about this need to control things. Or thinking they know how to guide a situation or guide a conversation. I think thats just an impression that comes off. Reporter so maybe some of that seemingly defensive or suspicious behavior can be explained by nathans aspergers. During our interview, its hard to get a full picture of him, in part because hes on edge after a crowd of media gathered, hoping to get to speak with him. As he got back in his truck, i head back to new york, haunted by one question. Just who is Nathan Carman anyway . Its time to dig deeper for an answer. Time to explore some dark and troubling secrets of nathans past. This wasnt the first time he was in the news. Patrol officer have been for Nathan Carman. Reporter when 20 20 continues. Big is here. Something bigger. And something. Smaller. Juicy. Lettucey. Oniony. Cheesy. Iconic big mac®. Now in three sizes, for a limited time only. Ba da ba ba ba listen, sugar, were lettin you go. Its that splenda naturals gal, isnt it . Coffee look, shes sweet, shes got natural stevia no bitter aftertaste and zero calories. All the partners agree . Even iced tea . Especially iced tea. Goodbye, sugar. Hello, new splenda naturals. Im Phil Mickelson pro golfer. 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