The document - originally from Granada’s police headquarters - refers to the one of the highest profile victims of the Spanish Civil War as a "freemason and socialist" as well as referring to his "homosexual practices".
It is the first time documents have come to light in which the Franco regime mentions the death of the poet, whose remains have never been found.
Lorca, who became famous for his poetry as well as his plays such as Blood Wedding and The House of Bernarda Alba, was murdered aged 38. It has been widely believed that he was executed by Spanish nationalists, but never once was it referred to during Franco’s subsequent 36 year dictatorship.
The document, seen by Spanish radio station Cadena Ser, referred to Lorca as engaging in the "aberration" of "homosexual practices".
It confirmed that Lorca was detained in the home of his friends, the Rosales brothers, and states that the property was surrounded by Republican Assault Guards at the time.
The police report describes how the poet was hiding in the house until he was arrested "at the end of July or beginning or August" 1936.
Lorca was "driven by nationalist forces to Viznar, Granada, close to an area known as Fuente Grande and, along with another detainee, was executed immediately after confessing".
The report also reveals that Lorca was "buried in a shallow grave in a ravine around two kilometres from Fuente Grande" in an area that would be "very difficult to locate".
Lorca was murdered in the first weeks of the Spanish Civil War, one of the most prominent figures to be killed.
In the last few years various searches have been undertaken to discover the exact burial site of the writer whose remains lie in an unmarked grave but all have proved fruitless.