Yves Bertrand was director of the "Renseignements generaux" from 1992 to 2004 -- an agency that kept tabs on individuals or organisations that could harm the state and that was sometimes accused of being a "secret police" organ as it was run by the national police.
One anonymous source told AFP the 69-year-old was found dead yesterday in his apartment in the chic 8th district of Paris by the building janitor, but was unable to say what caused his death.
The diaries, which revealed juicy rumours about the private and professional lives of politicians and other personalities, had previously been seized by authorities as part of a probe into the Clearstream affair.
That scandal erupted just ahead of the 2007 elections and centred on a fake list of names that falsely implicated then presidential candidate Nicolas Sarkozy in kickbacks on arms deals with Taiwan.
The "Renseignements generaux" no longer exist, having merged in 2008 with another agency to create the DCRI -- France's domestic intelligence service.