MARK STEVENSON,Associated Press
Tamaulipas has been plagued by drug cartel violence and is the home base of two warring cartels, the Gulf and Zetas drug gangs. There have long been suspicions that state officials may have favored the once-dominant Gulf cartel, but that has never been proven.
In a statement issued early Tuesday, the Attorney General's Office has not said why the former officials are being investigated, but by necessity it would involve federal crimes. Organized crime, drug trafficking and money laundering are all considered federal offenses in Mexico.
The statement did not name the officials, but three former Tamaulipas governors confirmed that they had been targeted in the probe. Eugenio Hernandez, who left office in 2010, told local media he did not know why he was under investigation, and denied any links to organized crime.
Tomas Yarrington, whose term ended in 2004, wrote in a Twitter account linked to his website that he had learned he had been named in the case, and said he hoped authorities would explain why.
Manuel Cavazos, who left office in 1999, called the investigation "suspicious ... coming in an election campaign," and suggested it might have political overtones. He denied any wrongdoing.
All the former governors are members of the Institutional Revolutionary Party, or PRI, which held Mexico'spresidency for 71 years until President Felipe Calderon's National Action Party won the 2000 presidential elections.
The PRI's de-facto presidential candidate, Enrique Pena Nieto, currently leads in polls ahead of the July 1 elections.
The mysterious probe came to light because prosecutors asked transportation authorities to keep track of when the ex-officials entered or left the country. Prosecutors never prevented the officials from leaving the country, and only asked local transportation authorities to advise the office when they did so.
But the Attorney General's Office said one airport official in Tamaulipas overstepped his authority and actually issued a memo seeking to keep those named in the investigation from leaving the country.
The Communications and Transportation Department said the official had been removed from his post.
Cavazos said "it would not be the first time that law enforcement has been used for political purposes, that has been done since 2000."
Cavazos is running for a seat in the Senate, and Pena Nieto was scheduled to visit Tamaulipas on Feb. 2, according to the PRI.
Still fresh in most Mexicans' memories are the mass arrests carried out by federal prosecutors of 12 mayors and 23 other officials in the western state of Michoacan in 2009. All 35 were later acquitted and released.
Michoacan is another state that allegedly served as a home base for drug cartels, and the officials were arrested on charges they had protected the Michoacan-based La Familia cartel.
Politicians have long been under pressure from cartels in Tamaulipas. In 2010, gunmen believed linked to one of the cartels ambushed a convoy carrying the leading PRI gubernatorial candidate, Rodolfo Torre, killing him and four of his companions. Torre's brother then ran for and won the governorship.