The Collaborative International Dictionary of English v.0.48:

Malefactor \Mal`e*fac"tor\, n. [L., fr. malefacere to do evil;
   male ill, evil + facere to do. See Malice, and Fact.]
   1. An evil doer; one who commits a crime; one subject to
      public prosecution and punishment; a criminal.
      [1913 Webster]

   2. One who does wrong by injuring another, although not a
      criminal. Opposite of benefactor. --H. Brooke. --Fuller.
      "Malefactors of great wealth." [1913 Webster +PJC]

   Syn: Evil doer; criminal; culprit; felon; convict.
        [1913 Webster]

WordNet (r) 3.0 (2006):

malefactor
    n 1: someone who has committed a crime or has been legally
         convicted of a crime [syn: criminal, felon, crook,
         outlaw, malefactor]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "malefactor":
   bad person, blackguard, criminal, crook, culprit, deceiver,
   delinquent, evil man, evil person, evildoer, felon, gangster,
   knave, lawbreaker, malevolent, malfeasant, malfeasor, miscreant,
   misdemeanant, misdemeanist, misfeasor, mobster, offender, outlaw,
   public enemy, racketeer, rascal, rogue, scoundrel, sinner, thief,
   transgressor, villain, worker of ill, wrongdoer



Bouvier's Law Dictionary, Revised 6th Ed (1856):

MALEFACTOR. He who bas been guilty of some crime; in another sense, one who
has been convicted of having committed a crime.



The Devil's Dictionary (1881-1906):

MALEFACTOR, n.  The chief factor in the progress of the human race.