Bernard Madoff’s longtime accountant pleaded guilty Tuesday to helping the jailed financier carry out the biggest investment fraud in history.

But David Friehling, 49, who kept Madoff’s books from a small office in Rockland County north of New York City, claimed in court that he was unaware that Madoff was running a Ponzi scheme. Nevertheless, he faces as much as 114 years in prison. He could get far less if he cooperates with investigators. 

Friehling was Madoff's auditor from 1989 to 2008. 

Friehling is the third person to plead guilty to criminal charges stemming from Madoff’s massive Ponzi scheme. Madoff and Frank DePasquale, who ran the phony investment firm Bernard L. Madoff Investment Securities with Madoff, are the others.

Prosecutors have alleged that Friehling had to know that Madoff was up to no good because Friehling was the sole auditor of Madoff’s financial statements. Essentially, Friehling is accused of rubber stamping his approval of those statements for nearly 20 years, a crime that helped Madoff’s fraud slip by the Securities and Exchange Commission and bilk investors of tens of billions of dollars.

Specifically, Friehling pleaded guilty to securities fraud, investment advisor fraud, making false filings with the SEC, and filing tax returns for Madoff and Madoff's associates that Friehling knew were false.

Prosecutors did not reveal for whom the phony tax returns were filed.

"In what was the biggest mistake of my life, I put my trust with Bernard Madoff," Friehling told Judge Alvin K. Hellerstein.

Friehling apologized to victims of Madoff's fraud, and continues to claim that he and his family lost all their investments with the disgraced financier. 

A tentative sentencing date was set for Feb. 26, but it was unlikely that Friehling will be sentenced until he completes his cooperation with prosecutors, which will include divulging any crimes by others he knows about and testifying before grand juries investigating the fraud.

Friehling remains free on $2.5 million bail.