Mexican authorities must immediately investigate an arson attack on the offices of a supplement owned by the daily El Norte, the third attack on an El Norte publication this month, the Committee to Protect Journalists said today. At least three vehicles pulled up outside the offices of Sierra Madre, in a suburb of the northern city of Monterrey, at around 6 p.m. on Sunday, according to news reports. At least two armed men entered the building and set fire to the lobby, news reports said. One employee was slightly injured while fleeing the attack, which caused extensive damage to the building, the reports said. CPJ's review of Sierra Madre's website shows that it covers local social events such as weddings and parties. On July 10, La Silla and Linda Vista, two other weekly social supplements of El Norte, were attacked by gunmen and with explosive devices, according to news reports. La Silla has been attacked four times since 2006, the daily Vanguardia reported. Both attacks remain unsolved. No motive was given for Sunday's attack, according to news reports. Local journalists told CPJ they believe the attacks on the three supplements were meant in retribution for critical reporting by El Norte on drug trafficking-related violence. It is unclear which El Norte story in particular could have motivated the attack. A video posted on the newspaper's website, which was taken at the scene of the crime, shows a police car arriving immediately after the assailants fled. Instead of pursuing the assailants, the police car turned around and drove away. "Each time Mexican authorities fail to effectively investigate an attack on the press, it emboldens assailants and fuels a new round of violent intimidation," said Carlos Lauría, CPJ's senior program coordinator for the Americas. "Authorities have a duty to prevent the criminals from controlling the streets and the flow of information--and they can start by solving this violent spree against the El Norte publications." Mexico is one of the world's most dangerous countries for the press, according to CPJ research. News outlets have frequently been subjected to attacks by assailants armed with guns and grenades, CPJ research shows. On the same day as the attacks on the two El Norte publications, the offices of the daily El Mañana in Nuevo Laredo were also hit by an explosive device, according to news reports. In March, a newspaper and TV station in the northeastern state of Tamaulipas were attacked within the space of one week, news reports said. CPJ