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When Nathan Carman, a Vermont man accused of killing his mother at sea over an inheritance, died by suicide, many believed he took his secrets to the grave.

But one true crime author believes that if the 29-year-old hadn’t killed himself in his jail cell, there wouldn’t have been enough evidence to convict him.

He argued that there were other suspects that could have been looked at, ones that Carman likely didn’t realize were present.

The aluminum boat used by Linda and Nathan Carman. (The Providence Journal-USA TODAY NETWORK via Imagn Images)

Sherman believes that Carman “could be a victim and a villain in his own story.”

“I do believe Nathan’s actions caused the sinking of that fishing boat where he made faulty repairs,” he explained. 

Signs supporting a safe return for Nathan and Linda Carman hang on the front porch of the family’s home on Sept. 28, 2016.  (Keith Bedford/The Boston Globe via Getty Images)

“I think that was negligence on his part. I don’t think that was criminally negligent… His brain worked in a way where he liked to take things apart and try to put them back together. For example, he purchased a historic farm home in Vermont. He had zero carpentry experience. He took that beautiful home apart in hopes of putting it back together. If you look at that house today, it looks like a big pile of Jenga blocks ready to collapse. Nathan didn’t know what he was doing.”

The Vermont home of Nathan Carman, circa 2016. (MediaNews Group/Boston Herald via Getty Images)

Sherman claimed that at least 15 witnesses saw Carman drill holes in his fishing boat and then tried to repair them himself. He said they also felt Carman didn’t know what he was doing.

Still, prosecutors said it was Carman who bought the rifle that he allegedly used to shoot his grandfather. They said Carman discarded his own computer’s hard drive and the GPS unit in his truck.

Following Nathan Carman’s death, his three aunts said in a statement that they were “deeply saddened” to hear about his passing and asked for privacy “while we process this shocking news and its impact on the tragic events surrounding the last several years.” (Nic Antaya for The Boston Globe via Getty Images)

Police also said Carman was the last person to see his grandfather alive and owned a semi-automatic rifle similar to the one used to kill Chakalos. That firearm disappeared. After Chakalos died, Carman received $550,000 from two bank accounts his grandfather had set up and that he was the beneficiary of when Chakalos died. 

The funeral urn of Nathan Carman is seen here. His cremains are buried next to his grandfather, Casey Sherman told Fox News Digital. (Lane Turner/The Boston Globe via Getty Images)

According to Sherman’s book, Carman’s cremains were buried next to his grandfather.

“I don’t believe he wouldn’t have been found guilty in a criminal court,” stressed Sherman. “However, I don’t know whether Nathan committed double murder. It depends on the day. Some days, I think he was a criminal mastermind. Other days I think there’s no way he could have pulled this off.”

Casey Sherman said Nathan Carman’s case will likely remain a mystery. (Suzanne Kreiter/The Boston Globe via Getty Images)

“I’ve covered 200 homicides in my career,” Sherman reflected. “It’s difficult to pull off the perfect crime, let alone two, one on land and one at sea… That may be giving Nathan more credit than he deserves.”