Peter Madoff, brother of shamed US financier Bernard Madoff, has been arrested and is expected to plead guilty to helping cook the books of the world's biggest ever Ponzi scheme.
"Peter Madoff played an essential enabling role in the largest investment fraud in US history. He made a pretense of compliance; he was really about complicity," said a statement from FBI Assistant Director Janice Fedarcyk.
FBI agents arrested Madoff at his lawyer's Manhattan office today. He was due in court later on Friday and expected to plead guilty to securities fraud, false declarations and falsifying documents.
Prosecutors say he has agreed to serve 10 years in prison and hand over his $US143.1 billion ($A142.98 billion) fortune.
"The Madoff investment empire, built on a foundation of deceit, was a house of cards that grew to skyscraper proportions," said the FBI's Fedarcyk.
"As Peter Madoff has admitted today, he was one of the chief architects. For decades he certified that periodic reviews established the firm's compliance with internal and regulatory rules," she said.
"In fact, Peter Madoff conducted no reviews. He certified that his examination of the firm's trading process established its integrity. He did not -- indeed, could not -- conduct any such examination: Despite the facade, the investment advisory business did not actually trade any stocks."
Bernard Madoff, a charismatic mogul and once chairman of the Nasdaq stock exchange, is serving a 150-year sentence at a North Carolina jail where he earns $170 a month for prison work.
He took in some $US65 billion ($A64.94 billion) from thousands of clients over decades, building a reputation as a shrewd investment manager by paying out fake "profits" to some investors by plundering the new cash from others.
Madoff counted charities, major banks, Hollywood moguls and savvy financial players among those who invested in his massive Ponzi investment scheme.
But his pyramid fraud collapsed in 2008, wiping out numerous family fortunes. He was arrested in December that year, and pleaded guilty in 2009.