Midrash sa Exodo 22:3: Sifra & Mekhilta DeRabbi Yishmael

1) (Vayikra 19:11) ("You shall not steal, and you shall not deny, and you shall not lie, one to another.") "You shall not steal": What is the intent of this (i.e., the prohibition against stealing has already been stated.) Because it is written in respect to stealing (Shemoth 22:6) "He shall pay double, we know the punishment. Where is the exhortation? (It is here,) "You shall not steal."

(Exodus 22:3) "If found will be found in his hand": in his possession. Even though there is no proof for this, there is support for it, viz. (Numbers 21:26) "and he took all his land from his hand", and (Genesis 24:10) "Then the servant took … and all the good of his master in his hand," — whence we find "in his hand" in all places to connote "in his possession."

"and it be stolen from the house of the man": to exempt (from kefel) one who steals from the thief. But perhaps the meaning is "and it be stolen from the house of the man, he pays double," but if it be found in his (the watcher's) possession, then even though he swore (that it was stolen), he is not liable (for kefel). It is, therefore, written (22:3) "If the theft be found in his hand, double shall he pay" — in any event (i.e., even if it were found in the watcher's possession. It is not the second assumption, then, which is to be posited, but the first, viz.: "and it be stolen from the hand of the man" — to exempt (from kefel) one who steals from the thief.