Which is correct?
The thief carried the knife carefully so as not to cut himself.
The thief carried the knife carefully not to cut himself.
I think the second alternative "The thief carried the knife carefully not to cut himself" is confusing, possibly incorrect. It would instead be used in this manner, I think:
The thief carried the knife carelessly, not to cut himself, but because he was in a hurry.
(And I replaced carefully with carelessly, otherwise the sentence would make no sense.)
Have a look at this explanation: http://forum.wordreference.com/showthread.php?t=698972&p=3849845#post3849845
I am not an English major but these answers seem wrong to me. I came here to see if "so as not to" was considered appropriate in any case. The comma makes it sound like the writer is trying to say that the killer was not suicidal and wasn't carrying the knife to intentionally cut himself. This is not what the author means. He means to say that the thief was carrying the knife in a protective manner so that it would not accidentally cut him. I would use, "The thief carried the knife carefully so that he would not cut himself."