Sullivan & Cromwell helped steer BNP Paribas SA to a historic guilty plea and settlement on Monday, bolstering the firm’s reputation as go-to counsel for banks locked in hostile negotiations with regulators. The deal could shed light on whether criminal penalties can undermine a modern bank’s viability or harm the economy at large, as some defense lawyers have argued in the years since the financial crisis.

In a criminal guilty plea unveiled on Monday in New York Supreme Court, BNP admitted to conspiring to help clients evade U.S. sanctions against Sudan, Iran and Cuba. BNP also agreed to forfeit $8.9 billion, the largest criminal penalty in U.S. history.

The deal is the culmination of an investigation the Manhattan district attorney’s office began in 2007. The U.S. attorney’s office in Manhattan and the New York Department of Financial Services later joined the investigation.

Sullivan & Cromwell partner Karen Patton Seymour represented BNP along with the firm’s senior chairman, H. Rodgin Cohen, the unofficial dean of the Wall Street bar. According to Bloomberg News, BNP hired Sullivan & Cromwell in mid-2013 to take over the lead role in the negotiations from longtime counsel Robert Bennett of Hogan Lovells. DealBook reported that BNP has also called on the services of Patrick Fitzgerald, a famed prosecutor who decamped for Skadden, Arps, Slate, Meagher & Flom in 2012.

France’s government lobbied unsuccessfully for a more lenient penalty, but U.S. regulators were clearly determined to make an example of BNP. New York Superintendent of Financial Services Benjamin Lawsky, one of the regulators at the negotiating table, has ramped up pressure on banks in recent years. And U.S. Attorney Preet Bharara has warmed up to the idea of imposing once-rare criminal penalties on banks, saying in a March 2014 speech that he’s skeptical of the argument that criminal penalties qualify as a death sentence for financial firms.

Last year Cohen and his colleagues at Sullivan & Cromwell advised JPMorgan in its $13 billion civil settlement with U.S. regulators. The deal resolved multiple investigations into the bank’s mortgage practices.