Not really. It is more complex than that.
There is two systems within the system for the "penal" (judiciary) in France:
- Le parquet, with a "procureur" who indirectly under the influence of the executive power.
- The "Juge d'Instruction". They are independent judges called only for complex affairs that are in charge of proof gathering and with more or less free hands.
Sarkozy affairs landed in the second system.
Politicans tend to hate the second systems for obvious reasons.
It is worth to notice that Sarkozy himself tried to reform the system and remove the "Juge d'instruction" entirely but ultimately failed.