Sam: If you saw someone shecht an animal in a democracy like Switzerland that outlawed shechita, you will testify in court against the shochet so they can throw him in prison?
Igros Moshe CM 1:8:
I received your letter with regard to an evil doer who came into a kosher factory and forged the kosher symbol, placed it on non-kosher items, which he sold to Jews as kosher. The question is can one inform on him to the secular authorities who will judge him severely with either a fine or prison, or must the rabbis judge him according to Jewish law? In my opinion, even though his sin is great, and he shows no repentance, nonetheless so long as we cannot say that the Jewish judges cannot judge him, one may not turn the matter over to the secular authorities… In addition, since it is certain that the secular authorities will adjudicate the matter through incarceration or a fine inconsistent with Jewish law, one must be fearful of the prohibition of informing, as it is prohibited to inform on a Jew to the secular authorities, whether through danger to his body or his money, even if he be a sinner.
Igros Moshe, OC 5:9 (11):
It is prohibited for us to inform on a person for a matter where the punishment is unfounded in Jewish law. In Jewish law, theft is resolved through restitution as measured by an expert, and secular law punishes through imprisonment, unfounded in Jewish law.
Chelkas Yaakov, CM 5 (or 3:96 in some editions):
One who looks in Shulchan Aruch and other decisors will see explicitly that there is no difference, and even when one who uses secular courts to reclaim his own, the matter is in dispute in Choshen Mishpat 388:5 and the Shach views such a person as an informer. A similar view is taken Brachos 58a concerning… [a person who slandered government] and such a person became a pursuer [to destroy the government] and he was killed. Even though it is certain that if a gentile had done the same thing and called the government bitter they would have punished him, still Rav Shelai considered him an informer (moser) and killed him; while it is true that this case is different in that Rav Shelai was certain that they would be punished for mocking the government. …. Even the money of a Jew, once it falls into the hands of a gentile, they show no mercy on it, as is quoted in Shulchan Aruch and other decisors, and as a matter of normative halacha this matter does not change … That which we have seen in recent times [the Holocaust] provides proof to this.