By Tony Hanson

PHILADELPHIA (CBS) — A sixth and final defendant has now pleaded guilty in a massive tax evasion conspiracy that spanned the existence of the Nifty Fifty’s restaurant chain until the scheme was uncovered in 2010. Former accountant William Frio has pleaded guilty and will be sentenced later.

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Frio has admitted to a scheme that began in 1986, lasted 24 years, involved owners, managers and others.

Prosecutor Nancy Potts says Frio and others already convicted skimmed cash, a lot of cash, paid by restaurant customers.

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Potts says the defendants failed to account for over $15 million dollars in gross receipts, evading taxes of over $2 million.

And Potts says Frio also helped himself and defendants cheat on their personal taxes as well.

“His job was in essence to zero out the tax burden for the businesses and the individuals.”

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Five other defendants pleaded earlier and were sentenced to prison terms ranging from one to three years in prison.