In "Retzei", human sacrifice is clearly mentioned:
רְצֵה ה' אֱלהֵינוּ בְּעַמְּךָ יִשרָאֵל וּבִתְפִלָּתָם וְהָשֵׁב אֶת הָעֲבודָה לִדְבִיר בֵּיתֶךָ. וְאִשֵּׁי יִשרָאֵל וּתְפִלָּתָם. בְּאַהֲבָה תְקַבֵּל בְּרָצון.
Restore the service to Your Sanctuary, and accept the humans of Israel and their prayers with love and with favor.
What were the details of these sacrifices? Who was chosen to be offered? How were they chosen? Could women be sacrificed too? What happened to their families? Etc.