My understanding is
- Halacha supports the use of the death penalty in theory but typically not in practice.
- The use of imprisonment as punishment is a recent development for Jews.
These two statements beg the question: What was the typical (or recommended) course of action for courts that had strong evidence that someone was a murderer, but not the enough for execution. Just lashes? It seems pretty dangerous to have a murderer wandering around after they recover.
Bonus points to anyone who knows of specific cases of how a beit din dealt with this.