Same word as malefactor:

bad egg, black sheep, con, convict, culprit, delinquent, evildoer, felon, hellhound, hoodlum, jailbird, lawbreaker, outcast, outlaw, prisoner, rapscallion, rascal, rogue, rounder, rowdy, ruffian, scamp, scoundrel, sinner, thug, transgressor, varlet, villain, wretch, wrongdoer