(CNN) -- Two bodies dangling from a pedestrian bridge in the border town of Nuevo Laredo, Mexico, created an image as gruesome as any in the four years of the country's offensive against the drug cartels.
A man and a woman, both in their early 20s, were left hanging like cuts of meat. The woman was hogtied and disemboweled, her intestines protruding from three deep cuts on her abdomen. She was then hung from the bridge by her feet and hands, topless. The bloodied man was suspended next to her by his hands, his right shoulder severed so deeply you can see the bone.
Two posters left near the bodies declared that the pair -- a young man and woman -- were killed for posting denouncements of drug cartel activities on a social network.
Bloggers who specialize in sharing news about trafficking have been threatened in the past, but this could be the first time that users of such social networks have been targeted.
The effect of such threats could be chilling, as several areas in Mexico -- including Nuevo Laredo -- have media outlets that self-censor out of fear of retribution by the cartels. In light of this censorship, blogs and social networks such as Twitter have surged as alternatives to keep citizens informed of dangers in their community.
Now the users of those networks appear to be under threat.
"This is going to happen to all of those posting funny things on the internet," one of the messages said. "You better (expletive) pay attention. I'm about to get you."
In the case of the two victims on the bridge, their ears and fingers were mutilated, said Ricardo Mancillas Castillo, an investigator for the public prosecutor's office.
There are no witnesses, and it is a nearly impossible task to identify the perpetrators, he told CNN.
In his four years based in Nuevo Laredo, Mancillas said he had never encountered a threat against Internet users. But the signs of torture -- the cuts, the disembowelment -- were along the lines of what officials are used to seeing in narco-related violence.
Thirty-six hours had passed since the bodies were found Tuesday morning, but no one had come to claim them and they remained unidentified, Mancillas said.
It will be nearly impossible to determine if the two victims actually posted anything about cartels on the Internet, as people don't usually use their real names online, he said.
The placards threatened those who report violent incidents through social media networks. It lists two blogs by name, Al Rojo Vivo and Blog del Narco.
They were signed "Z," a possible reference for the Zetas cartel, which operates in the area.
Blog del Narco is a website that deals exclusively with news related to drug violence in Mexico. Its creator remains anonymous.
On the Al Rojo Vivo forum, where citizens can make anonymous tips, one person wrote: "Don't be afraid to denounce. It's very difficult for them to find out who denounced. They only want to scare society."
One Twitter user echoed that sense of defiance in light of the threats.
"Enough! If we shut up today, we will have lost the ground that we have gained. This is the time to show what we are made of," the owner of the @QuestoyQuelotro Twitter account wrote.
In a statement sent to CNN, Blog del Narco said their site is not dedicated to denouncing crime, as are other sites.
"In addition, we are not in favor or against any criminal group, we only inform as things happen," the statement said.
CNN's Rafael Romo and journalist Raul Llamas contributed to this report.
