Pirates don't do public executions or trials. There's other institutions for that, historically.
Historically pirates had enough authority to commit public executions and much more.
As for
teenage mutant
ninja pirate
turtles ubers present in the mod they are proxy militant force which are paid for hostile actions towards major powers. There is some "t-word" identifying similar organisations in reality and, yes, they do perform public executions both historically and nowadays.
I'm not sure about currently present "robbery" logic but executions of hostages for infamy gain seems quite legit for me.