According to AP:
"On Sept. 21, 1976, agents of Chilean Gen. Augusto Pinochet planted a car bomb and exploded it on a Washington, D.C., street, killing both former Ambassador Orlando Letelier, and an American colleague, Ronni Karpen Moffitt. Letelier was one of the most outspoken critics of the Pinochet government."
Before this event the CIA and State Department officials were aware of the assassination aims of Chile against enemies of General Augusto Pinochet. Concerned, State Department staff sought to send a clear warning against conducting assassinations. They presented the proposal to Secretary of State Henry Kissinger for his decision.
Newly released State Department documents include a cable dated September 16, 1976. Under the SUBJECT: ACTIONS TAKEN, Subheading of "Operation Condor," AP reports:
The cable states that "secretary declined to approve message to Montevideo" Uruguay "and has instructed that no further action be taken on this matter."
The American silence, made official by Kissinger, was a green light.