Maimonides further explains: "It is forbidden to hand over a Jew to the heathen, neither his person nor his goods, even if he is wicked and a sinner, even if he causes distress and pain to fellow-Jews. Whoever hands over a Jew to the heathen has no part in the next world. It is permitted to kill a moser wherever he is. It is even permitted to kill him before he has handed over (a fellow Jew
https://en.wikipedia.org/wiki/Mesirah
Maimonides...one of the most important figures

https://www.chabad.org/library/article_cdo/aid/75991/jewish/Maimonides-His-Life-and-Works.htm