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A telephone scam artist picked the wrong target — former FBI chief and CIA boss William Webster.

Keniel Thomas, 29, from Jamaica, pleaded guilty in October to interstate communication with the intent to extort, federal authorities said.

He was sentenced to 71 months in prison last week by U.S. District Court Judge Beryl A. Howell in Washington, D.C., and will be deported after he has served his term, officials said.

Thomas made his first call to Webster on June 9, 2014, identifying himself as David Morgan. He said that he was the head of the Mega Millions lottery and that Webster was the winner of $15.5 million and a 2014 Mercedes Benz, according to court documents.

Little did Thomas know that he was targeting the man who had served as director of the FBI and then the CIA under Presidents Jimmy Carter and Ronald Reagan.

"It seemed to me that something wasn't quite right," Webster, 94, said in an interview Tuesday with "NBC Nightly News with Lester Holt." "This was pretty obvious to me that there was something fishy about it."

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Thomas told Webster and his wife, Lynda, that they must pay him $50,000 to cover the taxes on the prize, authorities said.

The Websters notified the FBI, and the agency recorded follow-up calls the couple had with Thomas.

Thomas later told the Websters that they had actually won a $72 million package. He began to grow impatient when they didn't pay him and began threatening them, saying he had been spying on the couple, prosecutors said.

"He terrified me," Lynda Webster told NBC News. "He told me that what the sniper's bullet would do to my head and the blood would go onto my white house."

The FBI eventually learned Thomas's identity and arrested him on Dec. 18, 2017, when he landed at JFK International Airport in New York, unaware he was a wanted man.

Lynda Webster said she and her husband have received calls from scammers in the past, but Thomas stood out.

"This is just one of many scammers that call him and call me. And what made this different though is that this particular gentleman was vile," she said. "He was nasty, he was frightening — terrifying is a word I use often. The others were nice and after I got involved or he got nasty with them, they gave up eventually. This one was different."

Lynda Webster said if she and her husband can be targeted, anyone is a potential victim.

"Everybody's vulnerable — every grandmother, every grandfather. I mean, I'm over 60 — I get called now," she said.

"They're very believable at first. And they're talking to people who probably in their age range would love to have a $1 million dollars or $50 million dollars. So, it's something they want to hear, `Oh I won some money.' It's very easy to fall prey to these terrible actors, I mean they're great actors, but they're terrible people."