hehe... for both of you:
first you have to look at all those other careers that base on working for government:
city guard, judge, lawyer
they\'re all lawful-neutral and that\'s because they follow law and orders given by their government.
The example given by TheRedMonk is same - the thief follows orders given by government.
I\'d like to point out that there wasn\'t mentioned that he believes stealing from evil and giving to poor is right thing to do, thus I don\'t see in what way he\'s good himself. Now if that was mentioned, he would be lawful-neutral by working for government and chaotic-good by believing stealing from evil and giving to poor is right thing to do.
All in all you could say he\'s either neutral-good (he believes in both law and chaos, yes strives to do good) or simply forget about alignments...