The brother of Ponzi fraudster Bernard Madoff has pleaded guilty to charges of conspiracy and falsifying records and has agreed to serve 10 years in prison.
Peter Madoff, 66, originally claimed he had not known his brother's securities business was a sham until it collapsed in 2008.
The BBC reports the FBI took him into custody at a lawyer's office in New York on Friday.
Bernard Madoff, 79, is serving a sentence of 150 years in prison after being convicted in 2009.
He has repeatedly denied that his brother had any involvement in his scheme, in which some $US20 billion worth of investments disappeared and a balance sheet of $US65 billion was revealed to be a sham.
Peter Madoff has been released on $US5 million bail, secured by $US1m in cash or property. He is scheduled to be formally sentenced on 4 October.
He told the judge in Mahattan Federal Court he had not known about the scandal until December 2008, when his brother admitted to it.