LEV474 [Many] sources point to the legitimacy of self-defense in Jewish thought and affirm the general concept of "if someone comes to slay you, you should slay him first" (Sanhedrin 72a). The concept of self-defense is extended even further in Judaism. Not only is a threatened person permitted to "take the law into his own hands" and kill the intruder or person threatening his life, but onlookers are also given permission to do the same, especially when the threatened person is unable to do it himself. Jewish law not only allows an onlooker to kill the attacker but commands the onlooker to take action (Sanhedrin 73a), based on [this] verse that a person may not stand by while his brother's blood is being spilled. Therefore, it is clear that the person whose life is threatened with attack must be protected, either by the person himself or by anyone who is in a position to prevent the loss of life.