In the northern Mexican city, at least 64 of these loyal pets, not counting stray dogs, have died since mid-March. All are believed to have been poisoned.
Some say the killer used an organic phosphate compound used as an insecticide, while others believe the chemical is rat poison.
Authorities have yet to find the killer, dubbing the person responsible the "Mataperros," or "The Dog Killer."
They are puzzled with this dog genocide that is hitting, not only dogs roaming free, but those kept behind fences as well, since poison was tossed onto the gated patios of some homes, the Associated Press reported.
— Noah Fairbanks (@NoahFairbanks) April 3, 2015
But why would someone want this loyal creature dead?
Someone called a local radio station and claimed responsibility for these brutal attacks, complaining about loose dogs, dog bites, and dogs spreading disease and uncleanliness.
But authorities did not buy these claims since some of the dogs that died were kept inside their owners’ homes.
Activists say one person couldn’t have possibly poisoned so many dogs.
"This is systematic. This can't be the work of one person alone," said animal rights activist Carolina De la Torre. "It could range from a neighbor who is bothered by noise (from pets), or even thieves who want to get rid of the dog in order to be able to break into the house," said De la Torre. "Those are the two theories we are looking at."
While killing a dog in Mexico is considered a non-serious crime, if caught, the killer would face a serious crime involving trespassing and risking human inhabitants for introducing poison into people’s homes, a crime that could carry a four-year sentence.