In 1971, Diaz was hired by the Bureau of Alcohol, Tobacco and Firearms (ATF) where he served as an undercover agent.

In 1975, Diaz was hired by the Drug Enforcement Administration (DEA) in New York City where he served 28 years as a special agent, 22 of which were spent working in an extensive undercover capacity.

[6] Diaz was also largely responsible for "taking down" all of the primary members of Barnes' drug trafficking organization known as the "Council."

This case involved the direct intervention of President Carter who ordered the then U.S. Attorney General, Griffin Bell, to see that Barnes was tried and convicted to the full extent of the law.

Diaz and his partner worked with members of Scotland Yard in London in pursuit of a gang of British criminals who were involved in the sale and distribution of large quantities of heroin.

During the course of this investigation, Diaz and his partner negotiated the sale of forty kilos of heroin with Ron Leslie, the principal subject.

During the course of the investigation, Diaz laundered over 50 million dollars for members of the Medellin cartel including Jose Lopez and Alfonso Reyes, who were close associates of Pablo Escobar.

According to the former U.S. Attorney General, Edwin Meese, Operation Pisces remains the largest most successful undercover drug investigation in the history of the United States.

[9][5][8][10] In 1988, the United States government, along with Victor Paz Estenssoro's government in Bolivia, launched Operation Blast Furnace, whose mission was to eradicate Bolivia's illegal coca producing fields and clandestine cocaine-producing laboratories located in the Chupari and Bene jungle regions.