In 1971, he was appointed ambassador to the United States by Chilean President Salvador Allende. Two years later, he served as Foreign Minister, and then Defense Minister. During the period, the CIA was actively engaged in an effort to destabilize the democratic government of Chile. This, together with serious mistakes by the chilean goverment ultimately led to the coup on September 11, which brought Pinochet to power. The United States then became strong supporter of new Chilean dictator.
As a result of the coup, Letelier was arrested by the Chilean dictatorship and tortured as a political prisoner. He was eventually sent to a political prison in Tierra del Fuego.
After his release, he went to Washington in 1974, where he worked for restoring democracy to Chile. He was killed by a car bomb explosion on September 21, 1976.
Several people were eventually prosecuted and convicted for the murder: Michael Townley, a US expatriot with close ties to the Chilean intelligence agency DINA; General Manuel Contreras, former head of the DINA; and Brigadier Pedro ESPINOZA Bravo, also formerly of DINA. Pinochet himself has never been brought to trial for the murders, although Townley has implicated Pinochet as having been behind them. Later released CIA documents showed that the CIA was closely linked with Contreras up to, and even after, the assasination of Letelier.
See also terrorism