NUEVO LAREDO, Mexico — A man who moderated a website denouncing drug violence on Mexico's northeast border was found beheaded Wednesday, local police said, in the fourth such apparent revenge attack since September.

Police found the decapitated, tortured body in Nuevo Laredo city alongside a message referring to his alleged activities on anti-crime website 'Nuevo Laredo en Vivo.'

The message said he was killed for "failing to understand I must not report on social networks."

Local police, who refused to be named, identified the man by his online name, 'Rascatripas,' or 'Fiddler,' but there was no immediate official comment.

A journalist who posted on the same website was found decapitated in September, two weeks after a man and woman were found hanging from a bridge in the same city with similar threats.

Press freedom groups have condemned growing attacks and killings of people who use social networks to share information in violent areas of Mexico where traditional media no longer dare to report on relentless drug-related violence.

Nuevo Laredo lies in Tamaulipas, once of Mexico's most violent states where the Zetas -- a brutal gang of former hitmen -- are fighting turf wars with their former employers the Gulf cartel and others.