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. :)