The killing of a Mexican woman purportedly in retaliation for her postings on an anti-crime website has left stunned chat users and employees at the newspaper where she worked wondering who can still be safe in the violent border city of Nuevo Laredo.

Press freedom groups condemned the killing of Maria Elizabeth Macias, whose decapitated body and head were found Saturday next to a message citing posts she wrote on "Nuevo Laredo en Vivo," a website used by Laredo residents to denounce crime and warn each other about drug cartel gunfights and roadblocks.

Some bloggers vowed to keep up the fight against powerful drug cartels but warned users to trust no one.

"If we want to regain our peace and our freedom, we always have to fight on, I wouldn't ask anybody to take up arms, clearly, but with our reports, we can do them damage," said one poster logged on as "anon9113," who quickly added a note of distrust, "don't become friends with anybody on here ... we have to be careful with something as simple as giving out personal information."

Another poster agreed. "Exactly, this (Macias' death) should not be in vain, we should make it an example." Others said that despite the risk, they would continue reporting. One user posted that he had seen four drug-gang lookouts in a compact car near a gas station, and gave part of the car's license plate number.

Macias had previously been identified by an official in Tamaulipas state as Marisol Macias, who had worked as a newsroom manager for the Nuevo Laredo newspaper Primera Hora. But an editor at Primera Hora said Monday that Macias was the daily's advertising supervisor. The editor would not give his name for security reasons.

The editor said the killing apparently was not related to Macias' job at the daily, which, in the face of intimidation and threats by drug gangs, had stopped even reporting on drug violence two years ago.

"We were taken by surprise, because since about two years ago, we don't even do crime reporting," said the editor. "We don't have a crime reporter."

He said police have not talked to the paper, nor given it any information on the killing. The paper, according to weekend editions posted on its website, has not even reported on her death.

Nuevo Laredo, located across the border from Laredo, Texas, has been dominated for about the last two years by the violent Zetas drug cartel.

Mexico's Human Rights Commission says eight journalists have been killed in the country this year and 74 since 2000.

With local newspapers forced to avoid crime reporting by threats in many border cities Mexicans have increasingly turned to local online chat sites like "Nuevo Laredo en Vivo" to report and read about cartel activity. The site includes numbers to phone in tips to police and the military.

The message found next to Macias' body on the side of a main thoroughfare Saturday referred to the nickname she purportedly used on the site, "La Nena de Laredo," or "Laredo Girl." Her head was found placed on a stone piling nearby.

"Nuevo Laredo en Vivo and social networking sites, I'm The Laredo Girl, and I'm here because of my reports, and yours," the message read. "For those who don't want to believe, this happened to me because of my actions, for believing in the army and the navy. Thank you for your attention, respectfully, Laredo Girl...ZZZZ."

The letter "Z" refers to the Zetas.

It was unclear how the killers found out her real identity; the newspaper editor said he did not know, but some posters suggested it could have been through someone she worked with.

The gruesome killing may be the third so far this month in which people in Nuevo Laredo were killed by a drug cartel for what they said on the internet.

Earlier this month, a man and a woman were found hanging from an overpass in Nuevo Laredo with a similar message threatening "this is what will happen" to internet users. However, it has not been clearly established whether the two had in fact ever posted any messages.

"As Mexican citizens, including journalists and media, are increasingly turning to new technology in the face of rampant censorship, drug cartels are using violence to control information on the Internet," Carlos Lauria, the Americas senior program coordinator for the New York-based Committee to Protect Journalists, wrote in a statement. "The stability of Mexico's democracy will ultimately depend on the restoration of the media's ability to report the news without fear of reprisal."

(This version CORRECTS Corrects in 10th paragraph that Nuevo Laredo is opposite Laredo, Texas instead of El Paso. This story is part of AP's general news and financial services.)