I would have asked Malfoy another question: By the time Harry allegedly cursed Bellatrix Lestrange, Lucius Malfoy was already in Albus Dumbledore's custody. How, then, did he mannage to speak with Lestrange and have her tell him what transpired in his absence?
I would also have taken the opportunity to inquire into the relations between Lucius Malfoy and one Baron Parkinson. And how come they spoke in length about things. And so on.
-mo