A dog seen carrying a human hand in its mouth sparked a harrowing discovery of 53 bin bags stuffed full of human remains.
Police found the mass grave as an international arts festival was in full swing in Guanajuato, Mexico.
The dog was reportedly followed by Bibian Mendoza, the founder of a women's collective searching for missing persons, with the pup leading the expert to the bags.
The festival - and the grim find - took place in October, and the remains have now been exhumed and analysed.
The founder of a women's collective searching for missing persons said: “While people from all over the world were celebrating the Cervantino festival, an international arts festival in the area, we were digging up bodies.
Mendoza told Agence France-Presse: "While people from all over the world were celebrating the Cervantino festival, an international arts festival in the area, we were digging up bodies.
"At the same time I thought it was useless because they were burying more people elsewhere."
It is not yet known how many of those have been identified, but it is thought that the experts are working with police to do so.
Between January and September this year, the area of Guanajuato has seen more than 2,400 murders as well as around 3,000 disappearances.
Officials have alleged that most of the issues – which, being in Mexico, are focused around cartels – are actually drug related.
The city is part of the “fentanyl and cocaine routes”, security expert David Saucedo said.
Many others in charge have promised to make the area safer, but Mendoza said: “Seeing bodies lying in the streets with messages is something new for us.
“I hate hearing the (state) governor say that he is going to deliver a safer Guanajuato. I hate hearing the president (Andres Manuel Lopez Obrador) say that what is happening is not his fault.”
The U.S. Department of State wrote in a travel advisory last month: "Gang violence, often associated with the theft of petroleum and natural gas from the state oil company and other suppliers, occurs in Guanajuato, primarily in the south and central areas of the state.
"Of particular concern is the high number of murders in the southern region of the state associated with cartel-related violence."
