That's up to a lot of things.

One thing is for sure, the PC has to start from somewere. So, I'd say that you can start by, for arguement's sake putting him the "Chaotic Evil" alignment, and then, depending on what the player shows you, you can change it; Just because he starts evil, it does not mean he is irependably evil... as you said, he might be evil, because he didn't know how else to act, but influence from the PCs might change him into a chaotic neutral character eventually. Or maybe his RP will suggest he was indeed that dumb that he never had any negative emotion inside of him when he commited those attrocities, and he literally just did them "for food", meaning you can safelly change his alignment to "unaligned". On the other hand, if he shows to enjoy (unessesary) bloodshed a bit too much, you know you went right on the alignment.

Finally, a piece of advice: Don't worry about starting Alignment too much... In game RP matters the most, and character development will eventually show what Alignment each character really is as sessions progress. Even if a character starts with the wrong alignment, it's not the end of the world, as long as he has an interesting Character development, and contributes to the plot (and not just to combat encounters). This Paralel Universe Orc (Warcraft Inspired I suppose?) can give you a lot of adventure hooks, and make for a very interesting story besides being just the muscles of the party. :)