Rav Wosner: Mandated reporting of crime is permitted - even if results in death

Rav Wosner(Shevet HaLevi 2:58): … Concerning the issue of reporting the tax cheat to the government see Bava Metzia (83b) concerning R’ Eliezer the son of Rav Shimon bar Yochai. The gemora reports that he reported thieves to the government. This is proof that where the government has authorized a Jew to report thieves that it is permitted. Even though he was criticized “how long are you handing the people of our G‑d to be killed” – because the punishment for thieves in those days was death. This is relevant also for a similar criticism from Eliyahu Hanavi to R’ Yishmael which is reported in that gemora. However the actual halacha seems that even when it results in the death penalty it is considered “the law of the land is the law.”  See the Ritva on that gemora which is found in the Shita Mekubetzes. …Also look at the Responsa of the Alshech who states that a person is not considered an informant for those things required by the law of the land….It is also obvious that this is not comparable to the case of R’ Eleazar ben R’ Shimon (Bava Metzia 83a) which involved danger to the person arrested. In contrast in our case here when they will just punish the person arrested and there is never a threat to life.