The Mishna in Sanhedrin 6:6 speaks about after a Sanhedrin kills a someone who is liable the death penalty:
והקרובים באים ושואלין בשלום הדיינים. ובשלום העדים. כלומר שאין בלבנו עליכם כלום. שדין אמת דנתם.
The relatives (of the deceased) would come and ask about the well-being of the Judges and the well-being of the the witnesses, meaning (the witnesses are saying) "that there is nothing in our hearts against you, for you delivered true judgement"
Is this statement of the Mishna a requirement for the family to abide to? Or was that the practice of the time?