A stack of declassified documents in April revealed that the late Mexican president José López Portillo, who governed from 1976 to 1982, had been a CIA asset “for several years” before taking office.

The serendipitous discovery in the recently released documents, which pertained to an investigation into the assassination of President John F. Kennedy, contained a memo in which US intelligence official Bill Sturbitts disclosed this information to colleagues. According to the memo, he had been “an informant in a ‘joint US-Mexico wiretapping operation,’” and “secretly recorded calls on dozens of telephone lines in the Mexican capital.” However, the details of López Portillo’s collaboration with the CIA remain mostly a mystery.

While the circumstances of the revelation came as a surprise, the fact that the former president had ties to US intelligence agencies didn’t — at least not for those familiar with the history of US-Mexico relations during the Cold War. López Portillo is the fourth Mexican president to have confirmed CIA ties in a lineage that includes all three of his immediate predecessors — Adolfo López Mateos (1958–1964), Gustavo Díaz Ordaz (1964–1970), and Luis Echeverría (1970–76) — all of whom governed during the Cold War and belonged to the Partido Revolucionario Institucional (PRI), which held power uninterrupted for seventy-one years.