Here is an épée d'un officier supérior du 3e cuirassiers – I imagine it to be from the same origin as the casque and cuirass.
By style, this armor is late period (1810-1815), which means colonels Richter, Lalaing d'Audenarde or de Lacroix.
The colonel baron Richter had the opportunity to order such an armor from late 1809 until his promotion to general in August 1811. But as a Swiss-born Protestant from a bourgeois family, he might have been hesitant to make such a lavish expenditure.
The comte de Lalaing, vicomted'Audenarde (titles inherited in 1806 upon the death of his father) was promoted colonel à la suite du 3e cuirassiers in January 1809 while serving as écuyer de l'impératrice Joséphine, and was made a baron de l'Empire in October. It would have been a perfect time to order high-end custom armor. From a rich noble faily, he could easily have afforded the expense. He became colonel titulaire of the regiment in September 1811 and was promoted a général de brigade de cuirassiers in December 1812. In December 1813 he was appointed major of the Red Lancers of the Imperial Guard and would have put aside his armor. He maaried Julienne-Nathalie Dupuy (1794-1849, fille du comte Dupuy), but the union bore no children, making a donation of relics to the Army Museum quite likely.
Colonel de Lacroix was promoted from major of the regiment in January 1813, in the midst of campaigning. He could only have ordered such up-scale armor during the 1st restoration, and would have worn it during the Cent Jours. As he was mortally wounded at Waterloo, it is unlikely that his armor made it to a museum in perfect condition.
So, I am thinking the armor was that of the comte de Lalaing.
