Aerial photographs at the beginning of the film and others that you can see over it, were digitalized by Israel Millan from photographs of Hector Garrido. This photographer has published a book, "Armonía fractal de Doñana y las marismas" (Fractal Harmony of Doñana and marshes) which includes some of the images used in the film. The images correspond to various marshes of Andalucia, such as the ones of Coto Doñana and the Salinas de San Fernando in Cádiz.
Some frames of the film are based on photographs of Atín Aya, whose work impressed the filmmakers when they knew his work in a retrospective exhibition.
The journalist asks whether Juan had been to Vallecas. Vallecas, a suburb of Madrid was the scene of resistance to Franco's regime, and thus a target for his secret police.
The coroner defines a bloodtype by examining sperm, however this technique was not yet available in 1980, but only since 1990.
Juan, according to the journalist, was a member of the Political-Social Brigade (Brigada Político-Social - BPS). This was a special branch of the plainclothes police.