In the beginning of the film, one of the revolutionaries tells a checkpoint security guard that his dead dog's name is Tupac. Tupac Amaru was the last indigenous leader of the Inca people in Peru and Tupac Amaru II was the leader of the 1780s uprising in colonial day Cusco, Peru. (The late hip-hop artist Tupac Shakur is named after the latter).
The story is inspired by the Maoist insurgency in Peru known as the Shining Path. Its leader Abimael Guzmán, who was known by the nom de guerre President Gonzalo, was captured in an apartment above a ballet studio in the capital Lima in 1992. The ballet teacher Yolanda was based on Maritza Garrido Lecca, the woman in whose apartment Guzmán was found. Bardem's character was inspired by Benedicto Jimenez and General Antonio Ketin Vidal, the leading figures responsible for Guzmán's capture.
The depiction of the dogs hanging was based on an actual occurrence where several dogs were found hanging from street lights in central Lima one December morning with profane messages denouncing Chinese leader Deng Xiaoping (who Guzman thought had betrayed the communist revolution). The dynamite inserted into the dogs' bodies was based on rumors that the hanging dogs may have contained explosives, though no explosives were actually found on the dogs when they were cut down.
The camera that Bardem uses to take Ezekiel's picture at the military checkpoint is a either a Polaroid Model 95 made from 1948 to 1953, or the Model 95B was discontinued in 1958. The picture that Bardem holds is a square format SX70 color shot identified buy its square format and black square on the back. This picture which could not have come from the camera used by Bardem.
There is a scene were Javier (the main cop) and Yolanda are talking about judging characters, Javier has the book in his hands. One shot, the camera is on Javier then goes back to Yolanda. In between those two shots, Yolanda's position changes.