Since the man did not mention the goblet, how were the brothers supposed to know what he was referring to?
Ramban and Seforno: He made out as if they knew what he was talking about (thereby implicating all of them - Seforno).
Why did he add the fact that it was the cup from which Yosef drank?
Ramban, Ha'amek Davar: This adds to their guilt, because someone who steals the cup from which the king drinks is guilty of despising the king, and bribery or payment will not be able to save them.
Hadar Zekenim: You should have known that he will immediately realize its loss, and know who took it through Nichush, or command others to find out who took it (Da'as Zekenim)!
Ohr ha'Chayim: He constantly drinks from it, so he immediately noticed its loss [and sent me to chase you].
Malbim: Refer to 44:4:152:1.
Why did he add, "v'Hu Nachesh Yenachesh Bo"?
Ramban: Because, not wanting his precious goblet to fall into the hands of others (they should have realized that) he was bound to consult the sorcerers, which is how he knew immediately that they had stolen it. This was to cover up how he knew that it was with them.
Rashi and Targum Onkelos: Refer to 44:15:2:1.
Rashbam: Refer to 44:15:2:2.
Ohr ha'Chayim: He knows the future through it - that you would steal it. This is why I do not suspect anyone else!
Malbim: Refer to 44:4:152:1.
Ha'amek Davar: He will be Menachesh for its sake (to get it back), and know immediately who took it. Nichush is common in Egypt!
Why did he say "Zeh"? He did not have the cup!
Riva: He had the base to which the cup was [initially] attached.
Ramban: He talked as if they knew what he was talking about (for they stole it).
He already said, "Why did you repay bad in return for good" (44:4), which is the ultimate evil. Why did he add "you did evil"?
Ohr ha'Chayim #1: Do not bring a proof [to your innocence] from the fact that you returned the first money. This evil breaks the Chazakah you made for yourselves. [Returning it] was happenstance. Sometimes thieves do nice acts, but not based on piety!
Ohr ha'Chayim #2: Returning the money was evil, in order to establish yourselves to be trustworthy, so people will trust you, and you will be able to steal things worth more than what you returned!
