Journalist Jose Cardenas released the text of the letter, which was sent to the family along with a photograph of Fernandez de Cevallos holding up a copy of the newsweekly Proceso.
I cant describe to you the hell your father is experiencing and I dont know how much longer I can take it. So I ask you to make your best efforts as quickly as possible, the captive said in the note, dated June 10 and addressed to his son, Diego.
They (the kidnappers) have all the time in the world, theyre in no hurry, he said.
Fernandez de Cevallos disappeared May 14 from his ranch near San Clemente, a town in the central state of Queretaro. The politicians vehicle was found at the entrance to the garage, with traces of blood inside.
The case was initially handled by the Queretaro Attorney Generals Office, with support from federal prosecutors.
The federal AGs office, however, said on May 22 that it was suspending its investigation in accord with the wishes of the family of Fernandez de Cevallos, a leading member of the ruling National Action Party, or PAN, and the partys presidential candidate in the 1994 elections.
A photo showing a much thinner and blindfolded Fernandez de Cevallos was released a few weeks ago by the kidnappers as proof that the politician was still alive.
In the letter released Monday, he asked his family to make a reasonable offer to the kidnappers and said that if the ransom demanded by the captors was too high, the family should make a counteroffer that demonstrates a will to negotiate.
It would be absurd and fatal for the family to plead poverty, Fernandez de Cevallos said, instructing his son to borrow money if necessary.
The captive reported chest pain connected with a recent heart operation, weight loss and increasing fatigue.
The mere passage of days will not move these gentlemen, but they will be favorably motivated if they clearly see your efforts (to amass the ransom), Fernandez de Cevallos told his son.
Whats urgent is to negotiate with complete seriousness to arrange the delivery of the money and my freedom, he concluded.
Mexican media say the kidnappers are demanding $30 million down from an initial demand for $50 million and that the Fernandez de Cevallos family has sold several vehicles, vacation properties and other assets.
Fernandez de Cevallos, who lost the 1994 presidential election to Ernesto Zedillo of the Institutional Revolutionary Party, has been one of the most powerful figures in the PAN and Mexican politics in the past two decades.
Known for his fiery oratory, Boss Diego was a member of the lower house of Congress from 1991 to 1994 and a senator from 2000 to 2006.
He also runs a successful law firm that has represented both Mexicos elite corporations and reputed drug kingpins. EFE