Shoftim #2: Double jeopardy

It turns out halacha has a concept of of double jeopardy - that once you have been acquitted of a crime, you cannot be tried for that same crime again. The yerushalmi sanhedrin had a derivation of this from psukim in Shemot. However, the sifrei has a nice derivation of this principle from the third pasuk in this week's parsha.

Devarim 16:20 states, צֶדֶק צֶדֶק, תִּרְדֹּף, "Justice, justice shalt thou follow." The full pasuk is:

צֶדֶק צֶדֶק, תִּרְדֹּף--לְמַעַן תִּחְיֶה וְיָרַשְׁתָּ אֶת-הָאָרֶץ, אֲשֶׁר-ה אֱלֹקֶיךָ נֹתֵן לָךְ.
"Justice, justice shalt thou follow, that thou mayest live, and inherit the land which the LORD thy God giveth thee."

צֶדֶק also denotes righteousness. First, the sifrei derives that even if someone has been condemned and they are leading him away to get capital punishment and he says he has new evidence or a new argument that would lead to acquittal, they take him back to be judged again. Further, they even will repeat this process one hundred times or more. They derive this from צֶדֶק צֶדֶק, תִּרְדֹּף. That is, righteousness (=innocence of the charges), righteousness you shall pursue. It says it two times to show you will pursue it even multiple times to get an acquittal.

However, the halacha is that once a man has been acquitted in a capital case, even if new evidence surfaces, or new witnesses appear, he cannot be retried. The sifrei gets it again from the same pasuk: צֶדֶק צֶדֶק, תִּרְדֹּף. Presumably the drasha is that only for acquittal - צֶדֶק - do you bring the case back to court, which implies that you don't to declare the man guilty.

I have an alternative suggestion to the one I proposed above as to how the sifrei understands the pasuk. We do not have to say that צֶדֶק = zakkai = innocent, but denotes judgement, showing that you will reconsider the case multiple times. There is a problem though: why retry it to declare the man innocent and save his life, but not to declare him guilty and thus take his life? Because the pasuk continues: לְמַעַן תִּחְיֶה, "that thou mayest live." That is, we will only reconsider the case so that he may live, by being acquitted, but not that he may die.