Gemara

(Mishnah): If Shimon claimed that Reuven's deposit was lost, and he swore falsely, and witnesses testify that Shimon ate it, he pays the value. If he swore that it was stolen, and witnesses testify that he ate it, he pays Kefel.

Inference: Kefel applies only to a claim of Geneivah, but not to a claim that it was lost. Even one who claims that it was stolen pays Kefel only if he swore!

107b (R. Chiya bar Yosef): One who claims that a deposit was stolen pays Kefel only if he was Shole'ach Yad (took it for his own needs).

He learns from "the Shomer... will swear that he was not Shole'ach Yad... (For any negligence, he pays Kefel)" implies that if he did take it, he pays Kefel.

Inference: This (Kefel) is only if he was Shole'ach Yad.

(R. Chiya bar Aba citing R. Yochanan): The case is, the deposited animal is at the feeding trough (he did not take it).

Question (R. Zeira): Does R. Yochanan teach that had he been Shole'ach Yad, he would be a Gazlan (not a Ganav), therefore he would not pay Kefel;

Or, does he teach that even if it is at the feeding trough, if he claims that it was stolen, he pays Kefel?

R. Chiya bar Aba: I did not hear about this, but I heard a similar case.

(R. Asi citing R. Yochanan): If he swore that it was lost, then swore that it was stolen, and witnesses testified that he had it, he does not pay Kefel.

Suggestion: This is because he acquired the deposit through his first oath (and owes principal. From then, it is his, so he cannot pay Kefel for it.)

Rejection: No. Rather, once he swore (that it was lost), he need not swear again, so the second oath is not considered a Shomer's oath to obligate Kefel.

R. Avin said so in the name of R. Yochanan.

(Rav Sheshes): If one claims that a deposit was stolen, and he took it (before he swore), he is exempt (from Kefel).

He learns from "he will come to the judges, if he was not Shole'ach Yad in his friend's object." This implies that if he did take it, he is exempt (from Kefel).

Question (Rav Nachman): He must make three oaths: that he was not negligent, that he was not Shole'ach Yad, and that it is not in his domain.

Suggestion: The last two oaths are similar. Just like he pays Kefel if we find that he swore falsely that it is not in his domain (for really, he stole it), also if we find that he swore falsely that he was not Shole'ach Yad!

Answer (Rav Sheshes): No, the first two oaths are similar. Just like if he swore falsely that he was not negligent, he (is like a Gazlan, who) does not pay Kefel, if he swore falsely that he was not Shole'ach Yad.

Rishonim

Rif (26b): If a Shomer (falsely) claimed that the item was stolen, he pays Kefel. This is only if he swore, and then witnesses came. If he did not swear, he pays only principal.

Question (Ba'al ha'Ma'or 37b): Why did the Rif omit the teaching of R. Chiya bar Aba? Even though we do not obligate fines nowadays, we must rule in case he seized (to know whether or not we force him to return it)!

Answer (Milchamos Hash-m): The fine applies only after a proper oath in Beis Din, which requires judges with Semichah. We have no such judges.

Mishneh l'Melech: Why did the Rosh and Tur bring this? Nowadays we do not judge Kefel (Beis Yosef CM 1:8 DH u'Mah she'Chosav umi'Lashon)!

Rambam (Hilchos Geneivah 4:1): If he swore that it was stolen from his house, and witnesses came and said that the deposit was with him, he pays Kefel, for he himself is the thief. If witnesses came before he swore, he pays only principal.

Rambam (2): This is when he swore before he was Shole'ach Yad. If he was Shole'ach Yad, swore that it was stolen and witnesses came, he is exempt from Kefel. Once he was Shole'ach Yad he became liable for it and acquired it.

Rebuttal (Ra'avad): This is not the Halachah, for R. Yochanan disagrees. He said that if he swore that it was lost, then swore that it was stolen, and witnesses came, he is exempt, for he exempted himself from the owner through the first oath. We do not say that he became a Gazlan and acquired it! Even though he acquired it like a Gazlan and is liable for Onsim, since he exempted himself through a claim of Geneivah, he is a Ganav and pays Kefel.

Magid Mishneh: The Rambam rules like Rav Sheshes, and also (Halachah 3) like this teaching of R. Yochanan. He holds that they do not disagree. Even though Shlichus Yad before the oath exempts from Kefel, it is not because he became a Gazlan. Rather, it is a Gezeras ha'Kasuv. Therefore, if he swore that it was lost, then swore that it was stolen, he would pays Kefel if we didn't say that the 1she is exempt oath exempts him from the owner. We do not exempt him became he became a Gazlan. As long as he was not Shole'ach Yad, it is in the owner's Reshus. Some, e.g. the Rashba, reject Rav Sheshes, for Rav Nachman challenged him. Perhaps Rav Nachman does not disagree; he merely wanted to hear Rav Sheshes' reasoning. Rav Sheshes answered the question! R. Chiya bar Aba holds like Rav Sheshes. Even though R. Zeira rejected this, he merely means that there is no proof from here. This is not enough to reject Rav Sheshes' teaching.

Rashba (107b DH Omar): The Halachah does not follow Rav Sheshes, who exempts one who he was Shole'ach Yad, for Rav Nachman challenged him. Perhaps also the Halachah is unlike R. Chiya bar Yosef, who argues with Rav Sheshes and exempts until he is Shole'ach Yad, for R. Chiya bar Aba said that R. Yochanan obligates when it was at the feeding trough. However, R. Chiya was unsure if R. Yochanan meant only in this case (but if he was Shole'ach Yad, he acquired), or even if it is at the feeding trough. However, we rejected this; he is exempt from Kefel because he exempted himself from the owner through the first oath. We support this; R. Yochanan himself said so, so the Halachah follows R. Chiya bar Yosef. Also R. Chananel says so.

Rosh (7:1): If a Shomer falsely claimed that the item was stolen, he pays Kefel.

Rosh (9:29): The Halachah does not follow R. Chiya bar Yosef or Rav Sheshes, rather, R. Chiya bar Aba. He pays Kefel even if it is at the feeding trough. If one who swore that it was lost, then swore that it was stolen, and witnesses came, he is exempt from Kefel, for his first oath exempted him from the owner. We do not exempt because he acquired it! This shows that the oath does not exempt and Shlichus Yad does not exempt.

Tosfos (107b DH Ho'il): Even though he admits that his first oath (that it was lost) was false, he need not swear again. He is believed to say that it was stolen, Migo (since) he could have said that it was lost and he is exempt. Even if Beis Din made him swear, e.g. another Beis Din that did not know that he already swore, he is exempt because he did not need to swear.

Poskim

Tur (CM 352): If one was Shole'ach Yad first, the Rambam exempts from Kefel even if he later swore and witnesses came. The Rosh says that he is liable.