The former controller for imprisoned financier Bernard Madoff blamed him Monday for directing her to deceive investors, regulators and the Internal Revenue Service as she pleaded guilty to conspiracy and other charges.

"I did not know that Madoff and others were stealing investors' money," Enrica Cotellessa-Pitz said as she entered the plea in U.S. District Court in Manhattan, becoming the sixth person to plead guilty and admit a role in a fraud that Madoff claimed he carried out alone. "For that, I am terribly sorry."

Cotellessa-Pitz , 53, said she wanted investors and the public to know that she is cooperating fully with prosecutors. Besides conspiracy, she pleaded guilty to falsifying books and records and making false filings with the Securities and Exchange Commission.

The charges carry a potential of up to 50 years in prison for a woman who admitted a major role in the multi-decade fraud that cheated thousands of investors out of the roughly $20 billion they invested with a man whose once-sterling reputation on Wall Street caused many people to feel honored to be allowed to rest their money with his private investment business.

Cotellessa-Pitz said she started working at Bernard L. Madoff Investment Securities LLC in 1978 while she was studying economics in college. She was named controller in late 1998. She said Madoff and others within months were directing her to put false entries in the company's books to make it appear profitable trades were being made and that losses were not incurred.