Why did they say "with whom you find the cup, he will die"? They should be concerned, just like their money was returned to their sacks, also the cup!
Rosh, Moshav Zekenim: They said so only if it will be found in his garment, 1 but not in his sack. The man claimed that it was a great offense to repay evil for good and steal from the king. Even if it will be found in his sack, he must be a slave.
We do not find that he checked their garments! Perhaps he would have done so had he not found it in a sack. (PF)
Why didn't Binyamin die from their curse? A Chacham's curse is fulfilled, even if it was based on a condition that was not fulfilled!
Moshav Zekenim #1: Binyamin did not die because he did not steal it. 1
Moshav Zekenim #2: They cursed only one that it will be found in his garment, but not in his sack.
Had they cursed the one who stole it, I would understand this. However, they cursed the one with whom it will be found, and it was found with Binyamin! This requires investigation. (PF)
Why did they say that the thief will die, and the rest will be slaves?
Ohr ha'Chayim: This is the law of a Ben Noach. He is killed for theft. We (the rest of us, voluntarily) obligate ourselves to be slaves.
Ha'amek Davar: The thief deserves to die for stealing from the king's house. We will be slaves for a fine, like one who joins with a thief, but not that we are suspected to all be thieves who know about the theft, Heaven forbid!
