A former trader at Bernard Madoff Investment Securities is expected to plead guilty next week to defrauding Madoff's customers by helping falsify records and fake trades starting in the early 1970s, federal prosecutors said in a letter Wednesday.

David Kugel, a former supervisory trader in the proprietary trading operations at Madoff's investment fund, will appear in Manhattan federal court on Monday, according to a letter sent to U.S. District Judge Laura Taylor Swain.

Kugel has been cooperating with the government in its investigation of Madoff and the fallout from what prosecutors said was a decades-long $65 billion Ponzi scheme, prosecutors said. His guilty plea comes as part of his deal with federal prosecutors in exchange for his cooperation, according to the letter.

He is being charged with taking part in a conspiracy to commit securities fraud, falsify broker-dealer records and create records of fake trades used to dupe clients of the fund's investment advisory business, prosecutors said.

Kugel also faces charges of bank fraud, securities fraud and falsifying records of an investment adviser and broker-dealer, prosecutors said.

Prosecutors said that Kugel began participating in the fraud starting in the early 1970s. That's several decades before Madoff admitted to have begun running his Ponzi scheme, which, he said during his guilty plea, started in the 1990s. An attorney for Kugel did not immediately return a request for comment Wednesday.

Kugel was one of several former Madoff employees sued by the trustee liquidating Madoff's investment management firm in 2010, seeking to recoup $70 million they allegedly withdrew improperly.

Madoff is serving a 150-year sentence in a North Carolina federal prison after admitting in 2009 to having run a decades-long Ponzi scheme.

The case is U.S. v. David Kugel, in the U.S. District Court for the Southern District of New York, no. 10-228.

(Reporting by Jessica Dye, editing by Bernard Orr)

(This story was corrected to fix the name of the judge in 2nd paragraph to Laura Taylor Swain from Laura Taylor Swift)