The manuscript was initially stored in Mexico’s national archives, but archivists microfilming the collection in 1993 found that 15 pages had gone missing.
The document is dated 20 February 1527, just days before one of Cortés’s top lieutenants was appointed co-governor of the conquered territory.
It was a key year for the formation of royal and religious institutions that would rule over the Indigenous peoples of Mexico until its 1810-21 war of independence.
Because the document has changed hands various times over the years, no one will be charged for the theft, the FBI said.
It is the second Cortés document the FBI has returned to the Mexican government. In 2023, the agency returned a 16th-century letter from Cortés.
