Assuming capital gain of a nonresident alien are not subject to

Since I am not a tax expert, all my reasoning are based on the assumption of following rules

capital gain of a foreign property of a nonresident alien are not subject to US tax.  Capital gain of a foreign property of a US resident alien and a US citizen are subject to US tax. 

Unless you find laws contradict above assumption, my argument is valid.  From 1999 to 2009 his status is a nonresident alien in US.  Therefore I don't see why he should pay capital gains from 1996 to 2009.

Again, check with a tax expert.  All the above are just some ideas I throw around. 

Lastly, thanks for your compliment, even though it is qualified. :)