To save everyone a google, the etymology of scot free is not based in Scottish juries.
The phrase in its oldest form literally refers to getting away without paying tax. Scot is cognate with the Danish (Scandinavian) word skat which means both tax and treasure - the latter meaning incidently being why it can be used as a term of endearment.
This later was broadened to mean getting away without any punishment. I could find no reference online to its use for show trials.
Sources:
https://www.etymonline.com/word/scot-free
https://www.phrases.org.uk/meanings/scot-free.html
https://www.theguardian.com/notesandqueries/query/0,5753,-27...