Dear Rav Kornfeld and Rav Weiner and all:
The mishna on daf 43a and the gemara discusses the various independent ways of valuing a stolen item.
If a thief stole an item, and another thief stole it from the first thief, and the second thief destroyed the item, how would the various approaches value how much the first thief owes the owner?
For example, if the item appreciated from time of first theft to time of second theft and further appreciated until the time of destruction, or depreciated in two steps, or appreciate and then depreciated, or depreciated and then appreciated?
I might think that the first thief bears responsibility for anything that happens following the first theft? But also from the first thief's perspective the item no longer exists from the time of the second theft.
And back to the theme of our gemara, if the first thief is really a borrower without permission, or a custodian who inadvertently moved the item from its established place, or utilized it in a way for other than the owner's benefit, but the second theft is not at all a type of borrowing...
Please reply with how this type of situation would be worked out.
According to the Gemara's conclusion both Beis Shammai and Beis Hillel agree with Raba.
If the item depreciates the thief always pays the original higher price. If the item appreciates it depends. If the thief actively destroyed the item (ate it, broke it, etc.) he pays the higher price. If he didn't harm it he pays the original lower price.
Is the negligence of the first thief which caused the second theft considered "active" destroying? The N'sivos HaMishpat 354:3 concludes that it is to be considered passive. Therefore the first thief will always pay the original price (when he stole) even when the price goes up.
In any case that he's legally a thief (like the borrower without permission) the same rules apply. (The calculations concerning the second thief are lengthly and involve many points.)
All the best,