Four masked thieves used a truck with a set of mechanical ladders mounted on it to gain access to the Gallery of Apollo via a balcony close to the River Seine at 09:30 on Sunday.
Two of them cut through a glass window on the first floor using a battery-powered disc cutter and entered the museum.
They then threatened the guards inside, who evacuated the building, and cut through the glass of two display cases containing jewels.
The thieves had tried to set fire to their vehicle outside but were prevented by the intervention of a member of museum staff. They were seen making off on scooters at 09:38.
The loot includes a diamond and emerald necklace Emperor Napoleon gave to his wife, a tiara worn by Empress Eugenie, the wife of Napoleon III, and several pieces previously owned by Queen Marie-Amelie.
Investigators also found a damaged crown that used to belong to Empress Eugenie on the thieves’ escape route – thought to have been dropped as they escaped.
Interior Minister Laurent Nunez told France’s Europe1 on Wednesday that he had “every confidence” the thieves would be caught.
Prosecutors have said their theory is that the robbers were under orders for a criminal organisation.