(Bloomberg) -- Federal prosecutors are trying to seize a $15 million fishing compound in Colorado and $77.9 million in a Swiss bank account linked to an alleged fraud by billionaire Robert Brockman, who was indicted last year in the biggest U.S. tax-evasion case ever against an individual.

Beyond claims that he failed to report $2 billion of income, Brockman is accused of using a foreign company he secretly controlled to buy secondary debt in his own software firm, Reynolds & Reynolds, at a deep discount in 2009. Prosecutors claim that assets tied to the debt fraud are subject to forfeiture, including a fishing lodge he developed on the Frying Pan River, according to U.S. court filings in March.

The targeting of cash in Switzerland’s Mirabaud Bank and 143 acres where Brockman has spent parts of his summers fly fishing for rainbow and brown trout are the only known attempts to take his property since he was indicted in October. The billionaire may be forced to turn over some assets even if a judge agrees with claims by Brockman’s attorneys that he isn’t competent to stand trial or he is found not guilty, said Peter Hardy, an attorney at Ballard Spahr who edits a blog about money laundering.

The government only has to show an asset was “the product of tainted funds” to take it in a civil forfeiture proceeding, said Hardy, who isn’t involved in the case.

In an asset-seizure affidavit filed by Internal Revenue Service special agent Ted Lair, the government alleges Brockman laundered some of his illicit proceeds through funds managed by Vista Equity Partners, a private equity firm run by Robert Smith.

Smith already has admitted illegally hiding some of his own income offshore but avoided prosecution for his crimes by agreeing to cooperate against Brockman and to pay $139 million in back taxes and penalties. Brockman “directed” that at least $1.6 billion be invested in Vista funds over 17 years, according to a Bloomberg analysis of the indictment against him. It’s unclear whether the entire amount was ultimately committed to Vista. The Lair affidavit indicates Smith was unaware of the alleged debt fraud involving Reynolds & Reynolds. A spokesman for Smith and Vista declined to comment.

A spokeswoman for the Justice Department declined to comment on the case. The U.S. first sought forfeiture of the Mirabaud account in October, leading a judge to issue a warrant for the account. Swiss prosecutors have frozen more than $1 billion held in bank accounts belonging to Brockman, Bloomberg reported in November.

Brockman, who turns 80 this month, pleaded not guilty to criminal charges and denies wrongdoing. His lawyers claim he has dementia and can’t aid in his defense. Prosecutors say he may be faking the illness, noting that Brockman stayed at Reynolds & Reynolds until after his October indictment and gave detailed answers in a deposition for an unrelated case weeks before a doctor examined him for dementia. A judge will decide if Brockman should stand trial in Houston, where he lives, after weighing the opinions of medical experts later this year.

A Brockman attorney declined to comment on the forfeiture proceedings.

Read More: Smith Avoided Tax Charge With Security, Barr Appeals

Fishing has long fascinated the billionaire, who has traveled widely in pursuit of his prey. His encrypted communications with people who helped manage his offshore trust structure included code names like “Redfish,” “Snapper” and “Steelhead,” prosecutors say.

Brockman frequently left his Texas residence to spend summers at a vacation home he owned outside Aspen. He built the fishing lodge on the Frying Pan River so that he and his guests could avoid the 30-minute drive from Aspen, according to the Lair affidavit.

Fisherman flock to the Frying Pan River from all over because it is “one of Colorado’s best trout streams,” said John Gierach, the author of “Sex, Death, and Fly-Fishing” and other acclaimed angling books. “If you’re a fisherman, it’s just a wonderful place to live.”

In 2010, Brockman arranged to acquire the Frying Pan River property in Basalt, Colorado, for $5 million, and he spent another $10 million on improvements to the river site, including building a lodge, according to the complaint.

Brockman’s land on the river is “stunning,” said Martha Cochran, former executive director of the Aspen Valley Land Trust, which holds a conservation easement on the property that bars development.

The government’s claim that property was acquired using illicit proceeds from the Reynolds & Reynolds debt deals is based in part on testimony by Evatt Tamine, a lawyer who managed Brockman’s offshore entities and is cooperating with prosecutors.

Tamine said he helped mask the billionaire’s ownership behind a limited liability company owned by a British Virgin Islands entity, Edge Capital Investments Ltd., court filings show. Edge has placed a claim on the $77.9 million in the Mirabaud account. A spokesman for Tamine declined to comment.

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