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.