A former trader at Dutch lender Rabobank pleaded guilty on Monday in federal court to conspiring to rig a key lending benchmark that underpins interest rates on trillions of dollars of financial contracts, from corporate debt to home mortgages.

Lee Stewart, 51 years old, who worked as a senior derivatives trader for Rabobank, admitted to conspiring to manipulate the London interbank offered rate, or Libor, between at least May 2006 and early 2011.