The Torah states: “Speak to Aaron and his children saying: This is the law of the hatath. In the place where you slaughter the olah slaughter the hatath before God it is the Holy of Holies” (Lev. 6:18).
Sotah 8:9. This is in accordance with that stated by Rabbi Levy according to Resh Lakish:Slaughter it before God – In order not to make public one’s sin”. One brings a hatath for severe sins that one commits unintentionally. One brings a ‘Olah for mere thoughts. God instructs Aaron and his children to bring both sacrifices in the same place so that on lookers do not have a way of telling how severely one sinned.
Amidah, where people would insert their own prayers and confess their sins was institute to be read quietly for the same reason.