Mexican authorities have identified 18 more suspects as they widen their investigation into last month's deadly arson attack on a Monterrey casino.Officials say those sought belong to the Zetas drug cartel and are offering 15m pesos ($1.2m) for information leading to each arrest.The blaze, which left 52 people dead, caused widespread revulsion in Mexico.It has also led to questions over the extent of links between casinos, local officials, police and drug gangs.Several people had already been arrested in connection with the fire on 25 August, including a police officer and five suspected members of the Zetas.On Wednesday, federal prosecutors named 18 more people sought in connection with the arson attack.They also released sketches of six of the suspects, identifying them by their nicknames including Commander Dog Killer.Several gunmen burst into Monterrey's Casino Royale in broad daylight, dousing it with fuel and setting it alight in what is thought to be a case related to extortion.Panic ensued with people inside struggling to reach the emergency exits or taking refuge in back offices or toilets. Many were overcome by smoke which spread rapidly through the building.The attack was one of the deadliest episodes of violence since President Felipe Calderon launched his crackdown on drug gangs in late 2006.Mexican authorities have identified 18 more suspects as they widen their investigation into last month's deadly arson attack on a Monterrey casino.Officials say those sought belong to the Zetas drug cartel and are offering 15m pesos ($1.2m) for information leading to each arrest.The blaze, which left 52 people dead, caused widespread revulsion in Mexico.It has also led to questions over the extent of links between casinos, local officials, police and drug gangs.Several people had already been arrested in connection with the fire on 25 August, including a police officer and five suspected members of the Zetas.On Wednesday, federal prosecutors named 18 more people sought in connection with the arson attack.They also released sketches of six of the suspects, identifying them by their nicknames including Commander Dog Killer.Several gunmen burst into Monterrey's Casino Royale in broad daylight, dousing it with fuel and setting it alight in what is thought to be a case related to extortion.Panic ensued with people inside struggling to reach the emergency exits or taking refuge in back offices or toilets. Many were overcome by smoke which spread rapidly through the building.The attack was one of the deadliest episodes of violence since President Felipe Calderon launched his crackdown on drug gangs in late 2006.The scandal took a further twist when a video subsequently emerged showing the brother of Monterrey Mayor Fernando Larrazabal receiving big wads of money at another casino.Manuel Jonas Larrazabal has denied any wrongdoing and says he was being paid for cheese and alcohol he sells.The mayor's own party, the National Action Party (PAN) of President Felipe Calderon, has asked him to step down while inquiries are under way.The PAN has also asked state governor Rodrigo Medina, who is from the Institutional Revolutionary Party (PRI) to temporarily step down.In response, a PRI spokesman David Penchyna told the Excelsior newspaper that the request was "media blackmail".Monterrey and the state of Nuevo Leon have seen rising violence as the Zetas and Gulf cartels vie for control of trafficking routes to the US.Some 40,000 people have been killed in drug-related violence across Mexico in the past five years. From/ BBC