If the Ganav is not found, the Shomer Chinam swears in front of Beis-Din and is Patur. What does he swear?
Rashi, Rashbam and Targum Yonasan: He swears that he did not take the article for his own personal use. 1
Ramban: He swears to substantiate his claim that it was stolen. 2 Gur Aryeh - Rashi on Pasuk 10 says so. Since the Torah suspects him of Shelichus Yad and makes him swear, he must also swear how it got lost.
Bava Kama, 53b: If the Ganav is not found, He swears that the article was stolen as per his claim. 3
Because if he did, it is akin to theft and he would be Chayav even for subsequent Onsin (Ramban and Seforno, citing Bava Kama, 63b). Refer also to 22:10:1:1.
"Im Lo Shalach Yado ... " is the condition that enables him to swear and be Patur, not a description of the Shevu'ah. See the final comment in Rav Chavel's footnotes.
Torah Temimah: The order of the statement in the Pasuk must be inverted
Seeing as Geneivah and Aveidah generally have the same Din with regard to Shomrim, what will be the Din if the Shomer claims that the article got lost, and is then found to have it in his possession?
Bava Kama, 63b: The word "ha'Ganav" exempts 'To'en Ta'anas Avad from paying Kefel.
What, in the event that the Ganav is found but is unable to pay, if the owner asks the Shomer to swear that he did not use the article?
Yerushalmi Shevu'os, 8:1. The Torah specifically obligates Shole'ach Yad by "Lo Nimtza ha'Ganav", but not where the Ganav is found.
On what condition does a Shomer become a Shole'ach Yad?
Bava Metzi'a, 43b: If he actually picks up the article with the intention of using it for himself
What are the implications of the sequence "Venikrav Ba'al-ha'Bayis el ha'Elokim Im Lo Shalach Yado bi'Meleches Re'eihu"?
Bava Kama, 107b: It implies that if the Shomer Chinam was Shole'ach Yad before he swore he is no longer Chayav Kefel like a To'en Ta'anas Ganav, since he became Chayav Onsin like a Gazlan.
What does Shelichus Yad entail?