If the thief (himself) were a Cohein, I might think that he acquires it. And this would follow a fortiori, viz.: If he acquires that of others, shall he not acquire what is his own! (That is, if others had stolen from the proselyte, who died without heirs, the Cohein acquires that theft. How much more so does he acquire the theft which he already possesses!) R. Nathan phrased it otherwise, viz.: If something which I do not acquire until it comes into my hand (i.e., ma'aser, and terumath ma'aser), another cannot acquire and take it from me, then something which I do acquire before it comes into my hand (i.e., what has been stolen from a proselyte without heirs), then when it does come into my hand, how much more so (does it follow) that another cannot acquire it and take it from me! — No, this may be true of something which he does not acquire until it comes into his hand, for just as he has no portion in it, so, others have no portion in it.
But would you say the same for this (what has been stolen from a proselyte)? Just as he has a portion in it, so, others have a portion in it, and since this is so, it follows that it should be taken from his hand and be apportioned among the men of the officiating watch.