A senior partner at a New York accounting firm pleaded guilty to criminal charges Tuesday in a cooperation deal with the government, saying he unwittingly played a role in financier Bernard Madoff’s “horrific and evil Ponzi scheme.”

Paul Konigsberg, a 78-year-old accounting firm executive, pleaded guilty to conspiracy and two counts of falsifying books and records in federal court in Manhattan. He also agreed to forfeit $4.4 million in cash and property. Sentencing was set for Sept. 19.

The Southern District U.S. Attorney’s office said he was the only person outside the Madoff family to have held an ownership interest in the private investment business before it was exposed in 2008 as a gigantic decades-old fraud.

Madoff, now serving a 150-year prison sentence, admitted in 2009 that claims he managed up to $68 billion for investors were false because he had squandered all but a few hundred million dollars of roughly $20 billion entrusted to him.

Konigsberg told Southern District Judge Laura Taylor Swain (See Profile) that he sometimes agreed with employees to return trading statements to Madoff’s firm so that the employees could change information about securities that had been traded. He said he did not know, though, that the substituted trades t had not occurred. “I was not aware of Madoff’s horrific and evil Ponzi scheme,” he said.

Konigsberg, of Greenwich, Conn., was a senior tax partner at Konigsberg Wolf & Co. when he worked for some of Madoff’s most important clients, beginning in at least the early 1990s, Assistant U.S. Attorney Matthew Schwartz said.

By the time the fraud was discovered, Schwartz said, Konigsberg handled more than 300 of Madoff’s private securities accounts.