The brother of a U.S. Marine veteran who was arrested Russia on accusations of espionage said Monday that his sibling exhibited no signs of being a spy.

Paul Whelan could reportedly face up to 20 years in prison if convicted of the crime.

"Paul's case proves that truth can be stranger than fiction," his brother David said on "Shepard Smith Reporting," noting reports that his brother may have been arrested as a tourist in a sting operation.

He said that he knew his brother had friends in Russia, and that it wasn't surprising some of those friends were in the military.

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He added that his brother holds numerous passports because of how many times his family has emigrated.

"It's so hard to know," he said. "He has no sign that he would ever be hired as a spy."

Paul Whelan was in Moscow on Dec. 28 to attend a wedding of a friend from the Marines when he was arrested.

He was reportedly given a USB stick minutes before his arrest at a hotel, which contained the names of individuals working at a Russian security agency.

David added that it was "rewarding" to hear from Jonathan Huntsman, U.S. Ambassador to Russia, who met with Whelan in Moscow last week.

"We've started to get information from Paul about next steps to try and help him," David said.

Watch the full interview above.

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