Underwood took him to court and won but he still won’t pay. With everything to gain and nothing to lose, Underwood has taken to disguise to find out where Drakulic's money is.

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A Love Story Begins

Katherine Underwood was a coat-check girl working in Aspen, Colorado, when she met Budimir Drakulic, a scientist with several Ph.D.s travelling on vacation.

Drakulic professed his love for Underwood on the first night they met, but true love soon turned into true greed.

He began asking Underwood for money to finance his work as a scientist, and over the course of their six-year relationship, drained Underwood’s bank account dry, borrowing more than $400,000 from her and spinning a web of lies and deception that Underwood says she has spent years trying to unravel.

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Web of Lies

Throughout their relationship from 1994 to 2000, Underwood said Drakulic told her he was working at Edwards Air Force Base in the California desert. In reality, the last time he had been on the base was in 1993.

In 2000, Underwood became becoming suspicious when Drakulic called to tell her he was working on a top-secret government project at Edwards, but the caller ID said Los Angeles. That’s when she suspected Drakulic was lying to her.

“I called the operator. She thought that was a Beverly Hills pay [phone],” she said. “Then I knew I was in trouble. I felt stupid.”

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Uncovering the Truth

Underwood hurried to Los Angeles and found her proof: Drakulic wasn’t working in the desert or on a secret project.

He was taking a private tennis lesson in Los Angeles.

“He was a liar,” Underwood said. “He wanted me to leave and [told] me that I have no business coming to Los Angeles unannounced.”

Katherine Underwood

In Disguise

Underwood filed a lawsuit against Drakulic.

She was granted a judgment and is now owed more than $1.6 million.

But Drakulic filed for bankruptcy and refused to pay.

Out of money to hire lawyers, she began conducting her own surveillance, including dressing in disguise, in an attempt to locate Drakulic’s assets.

Katherine Underwood

Under Surveillance

Underwood told "20/20" about a time when she sat next to Drakulic at a restaurant and heard him discussing the case just feet away.

“One time that I sat so close that the waiter came up to ask me for my order, and I couldn’t talk to him,” she said. “I heard [Drakulic] say that they had outsmarted us.”

But no amount of surveillance and digging could get Drakulic to repay his debts. The elusive scientist seemingly had no assets in his name, making it close to impossible to claim that he had the money to pay her back.

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Private Investigator on the Case

Bob Nygaard discovered that Drakulic was earning big bucks.

A private investigator who specializes in playing hide-and-seek with people who don’t want to be found, Nygaard discovered that Drakulic was making close to a quarter of a million dollars per year.

“She’s owed a fortune and she can’t collect a single cent because this guy’s playing games,” he told ABC News' "20/20." “Talk about adding insult to injury. It really is a travesty of justice.”

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The Last Attempt

Another professional is now on the case. Nelson Tucker, a process server, went to Drakulic’s workplace seeking to garnish his wages.

It’s a last attempt at getting Underwood her money back: If Drakulic fails to respond to the court order within the next week, his employer must legally deduct 25 percent of his income and send it to the L.A. Sheriff’s office for Underwood.

"It doesn’t go away,” Tucker told "20/20." “It just keeps getting larger and larger, which is putting him deeper and deeper in the hole."

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Underwood's ex-boyfriend Drakulic is seen here during surveillance.

Still Searching for Answers

For Underwood, gone is the man that swept her off her feet 20 years ago.

“Could you do that to someone you cared about? I don't think so,” said Underwood.