Slow death by piranha. One limb a day. Propane torch should keep them from bleeding to death.
First a slow hanging, then drawn (disemboweled),
then beheaded (if possible while still alive),
their bodies then quartered (cut in to 4 pieces) those pieces then sent to four locations to be put on display with a written explanation as how these men came to their fate as a message to those that would perform similar acts.
Their heads should them be put on display at gates to the capital city with the same written explanation.