The memorial is on Sheridan Circle near Embassy Row and Massachusetts Ave, NW. From Wikipedia:
“On September 21, 1976, Orlando Letelier and Ronni Karpen Moffitt were killed by a car bomb in the circle. Letelier had been foreign minister in the ousted Allende government of Chile.
The bombing was blamed on Chilean DINA agents. Michael Townley, a DINA U.S. expatriate among those convicted for the crime, confessed that he had hired five anti-Castro Cuban exiles to booby-trap Letelier’s car. According to Jean-Guy Allard, after consultations with the Coordination of United Revolutionary Organizations leadership (including Luis Posada Carriles and Orlando Bosch), those selected to carry out the murder were Cuban-Americans José Dionisio Suárez, Virgilio Paz Romero, Alvin Ross Díaz and brothers Guillermo and Ignacio Novo Sampoll. According to the Miami Herald, Luis Posada Carriles was at the meeting that decided on Letelier’s death and also about the Cubana bombing two weeks later.”