By Clare Marshall
BBC News, Mexico City
A top aide to Mexico's President Vicente Fox, who was accused of links to a drugs gang, has had charges against him dismissed.
Mr Fox has vowed to crack down on organised crime
Nahum Acosta, the former head of Vicente Fox's travel staff, could soon be released from prison unless new charges are filed.
He was charged with passing details of Mr Fox's travel plans to a drug gang.
But a judge has thrown the case out, saying there was not enough proof to link him to a criminal organisation.
When he was arrested in February, it was claimed that the drug bosses had managed to infiltrate to the highest levels of the government and that an assassination attempt on Mexico's leader was being planned.
The evidence supplied included a recorded telephone conversation about an alleged delivery of $5,000 to Mr Acosta and other exchanges with known narco-traffickers.
President Fox has been waging what he calls the mother of all battles against organised crime.
Several top cartel leaders have been arrested.
However, drug related violence has soared across the country as second tier gangs fight for control of the multi-billion-dollar trade.