Regarding mesira - informing on other Jews: If someone witnessed another Jew committing what the secular authorities consider a crime, is it permitted to report them to non-Jewish or secular Jewish authorities? The prohibition of being a moser is extremely severe. Even if the person violated the law of the land, you are absolutely forbidden from informing on them. The spiritual consequences are truly immense, and you would be losing your Olam Haba.

Mesira, informing on a fellow Jew to non-Jewish authorities, is an extremely severe transgression leading to the loss of one's share in the World to Come. It is strictly forbidden for monetary or business disputes, which must be resolved by a Beit Din. However, if an individual poses a physical or spiritual danger to the community (e.g., violent criminals, abusers), reporting them is a mitzvah to protect others. The key distinction is whether the matter is a communal threat or a dispute resolvable through Torah law.