White collar and finance-related investigations & litigation
Rebecca Mermelstein is a first-chair trial lawyer with extensive experience handling white collar and finance-related investigations and litigation. She advises corporate and individual clients on complex white collar matters, including regulatory actions, internal investigations, and compliance initiatives.
Prior to joining O’Melveny, Rebecca spent more than a decade as an Assistant U.S. Attorney in the U.S. Attorney’s Office for the Southern District of New York. She was a senior member of the Securities and Commodities Task Force before rising to Co-Chief of the General Crimes Unit. Rebecca has tried 12 cases to verdict, briefed and argued numerous federal appeals, and conducted or supervised more than 1,000 investigations, including grand jury investigations and cross-border matters involving simultaneous investigations by multiple U.S. and international regulators. Her expertise spans securities and accounting fraud, insider trading, Ponzi schemes, money laundering, cybercrime, public corruption, human trafficking, and sexual misconduct.
Through her work leading investigations and prosecutions, Rebecca has established strong working relationships with U.S. Attorney’s Office colleagues and officials at the Securities and Exchange Commission, Commodity Futures Trading Commission, and the Public Company Accounting Oversight Board, as well as federal law enforcement agencies. The knowledge she has gained from her experience and relationships helps her achieve the best possible results for clients.
O'Melveny & Myers LLP
New York, New York
U.S. Attorney’s Office, General Crimes Unit
(appointed)New York Southern District
Simpson Thacher & Bartlett LLP
New York, New York
U.S. District Court
(appointed)New York
Served as judicial law clerk to the Honorable Charles P. Sifton, researching and drafting opinions, orders, and bench memoranda.
U.S. Attorney’s Office
(appointed)New York Southern District
March 2025
Represent a global commodities trading company in a wide-ranging FCPA investigation by the United States Attorney’s Office for the Eastern District of New York and Main Justice involving alleged conduct in South America. Represent a Fortune 50 company in a DOJ investigation under the False Claims Act. Represented an entertainment company in an internal investigation of senior officers concerning possible violations of internal finance and approval policies. Represented a global consulting firm in an in internal investigation and litigation relating to allegations under the Adult Survivors Act. Secured an acquittal for a Louisiana man who served more than eight years in prison after he was wrongfully convicted of second-degree murder by a non-unanimous jury.
March 2025
Supervised dozens of jury trials and more than 1,000 cases involving securities fraud, wire fraud, mail fraud, tax fraud, money laundering, access device fraud, cybercrime, immigration offenses, child exploitation, human trafficking, robbery, narcotics trafficking, and firearms offenses. Investigated and prosecuted complex financial crimes, including accounting fraud, insider trading, market manipulation, investment adviser fraud, wire fraud, bank fraud, insurance fraud, and money laundering. Managed relationships with FBI and SEC, among other agencies. Conducted 12 criminal trials, including numerous multi-defendant white-collar cases. Briefed and/or argued more than a dozen appeals in the Second Circuit. Investigated, prosecuted, and supervised numerous sex-crimes cases, including leading the investigation and prosecution of a 19-defendant international sex-trafficking ring and supervising multiple cases of sex abuse by middle school and high school teachers.
The Legal 500 US
January 2024
New York Law Journal
March 2023
Co-author
Bloomberg — Podcast
March 2024
O’Melveny partner Rebecca Mermelstein was featured on Bloomberg Television to discuss the sentencing of Sam Bankman-Fried, who was convicted of fraud. “I think that you saw the government weaponize the defense theory here. The defense tried to use his autism, his inability to experience happiness, and his effective altruism that he was so committed to, to explain, if not justify some of the actions he took and to cast him in a more sympathetic light,” Mermelstein said. “What the government did was flip that coin on its head and say that is exactly why this defendant is so dangerous and why he needs to be not just punished, but incapacitated and incarcerated for a long enough period of time so that he won't be able to commit future crimes.”
Michael Lewis — Podcast
September 2023
O’Melveny partner Rebecca Mermelstein was featured on an episode of the “Against the Rules” podcast, hosted by bestselling author Michael Lewis. Mermelstein and Lewis discuss the case against Sam Bankman-Fried, the former CEO of crypto firm FTX. With Bankman-Fried’s trial set to begin next month, Lewis taps Mermelstein’s insights as a former prosecutor on how prosecutors are building their case and how the defense team might prepare.