Mesira (Informer): Tax Auditor?

 Rambam(Chovel u’Mazik 8:10) An informer may be slain anywhere, even at the present time when Jewish courts do not try capital cases. It is permissible to slay him before he has informed

Shulchan Aruch (C M 388:12) All those who inform against the community and distress it can be given over to the government through non Jews even though they will be beaten and imprisoned but it is prohibited for the sake of the disress of an individual

Semah (30) but it is prohibited for the sake of the disress of an individual – this is prohibited only for general distressing. However If the informant is causing a monetary loss  and surely if he is causing torture or physical punishment it is permitted

Aruch HaShulchan (CM 388:7) Historically it is well known that in previous ages  in times of old in far away places, no person had any assurance in the safety of his life or money because of the pirates and bandits even with government assurances. It is known that this is true even today in some places in Africa where the government itself is corrupt. One should remind people of the kingdoms in Europe and particularly our ruler the Czar of Russia and his ancestors as well as the the kings of England, who spread their influence over many lands in order that people should have confidence in the security of their body and money. The wealthy no longer have to conceal themselves so that they  will not be robbed or killed. The prohibition of informing in fact depends on the existence of lawlessness in the Talmud and poskim. In other words the prohibition is only not to inform on another to bandits which endangers that person's money and life but not to a just legal system. Bandits chase after the person's body and money

Igros Moshe (CM I #92) Question: Is it permitted to take the job of government tax auditor since it might result in someone getting criminal punishment for cheating and thus he becomes an informant? Answer You are concerned about discovering cheating that will be punished more severely than Torah law. This is a valid concern since an auditor’s job is to find cheating. However it is certain that if you don’t take the job there will be  others who will, and thus there it makes no difference to the tax cheat since he will be caught anyway.In other words there is no unique harm to the tax cheat if you take the job and without the unique harm there is no prohibition. Furthermore most of his work involves accounts which don’t contain illegal activity. Therefore he doesn’t work on the basis that he will find illegal activity and he simply assumes that each account will be legal though there is a possibility that it might be illegal. Such a job is not prohibited just because of the possibility that he will sometimes discover illegal activity. If he discovers illegal activity he is obviously forced to tell the truth because other wise it would create a chillul HaShem