As Search for Man Lost in River Goes on, Skepticism Grows

When Roberson visited Matthew Sheppard's employer, the Eaton Corp., in Searcy, he found auditors at the company had recently uncovered $40,000 in unauthorized charges on Sheppard's company credit card. The charges were for everything from gas to gadgets, and even a washer and dryer.

Roberson also discovered that Sheppard had raised his life insurance policy to the company maximum one month before his accidental drowning. Monica Sheppard now stood to collect more than $1 million in insurance money from her husband's untimely death.

As Roberson continued to dig, he found there was a darker side to the seemingly well-liked and affable Matthew Sheppard. Although he made a good salary, Sheppard was deep in debt. While at Eaton, he had used two different Social Security numbers -- and he had a criminal history.

"There were forgeries, auto theft, and theft of government property," Roberson said.

Matthew Sheppard: Vanished

Confused by Monica's behavior and with his suspicions growing about Matt, Roberson issued a nationwide missing persons alert for Matthew Sheppard. He also asked U.S. customs to be on the lookout for Sheppard's passport and contacted a host of other government agencies as well.

"We contacted criminal investigations with the IRS, put him in every database you can find, but nothing. He vanished into thin air," Roberson said.

One week after Sheppard's disappearance, Roberson uncovered something: Phone records revealed that Sheppard's company-issued cell phone had sent text messages hours after he supposedly drowned.

"The numbers we checked turned out to be pre-paid cells. They're basically untraceable," Roberson said. "And text messages, all you can get is the numbers. You can't get content. At that point, I was pretty well convinced that he wasn't dead."

With a dogged detective who was unwilling to accept that this drowning was a simple accident, the question now became: Would Matt Sheppard ever be found, dead or alive?

Watch the full story Tuesday on "Primetime: Family Secrets" at 10 p.m. ET