In the later (Moldvay and Mentzer) editions of the Basic game, they could be Neutral or Chaotic, but not Lawful; also they had to be Human, even in the Holmes edition.
In the later (Moldvay and Mentzer) editions of the Basic game, they could be any of the three available alignment options (Lawful, Neutral and Chaotic). Thieves had to be Human, even in the Holmes edition.