Parshat Mishpatim discusses the liability of various watchmen over other people’s property. They are known as the four שומרים, or guards.
Each one has a different level of responsibility. The borrower and renter have the most obligations to the owner of the object they are using. There is the paid watchman, שומר שכר, who must reimburse in the event of theft.
The שומר with the least liability is the שומר חינם, the one who guards for free. He only pays for negligence and does not pay in the event of theft.
The Baal Haturim comments that the Gematria, numerical value of the words, אם לא ימצא הגנב, “If the thief will not be found,” is equal to the words, הוא עצמו הגנב, “He, himself, is the thief!”
This is truly amazing how the Baal Haturim figured this out. If an article was stolen, as the שומר חינם claims, he becomes the prime suspect. The remedy of the Torah to get to the truth, is to demand a biblical oath, known as שבועה.
The suspect must swear using G-d’s name, while holding on to a Torah scroll, that he is innocent.
The hope was that the oath taken in such a manner, will impress the need to tell the truth. There is no better system of civil law than that provided by the Torah.