[sp332]

Any profit he stands to make in the years following will be taxed according to the laws of his new residence.

[xiaoma]

As itsmequinn said, tax free.

http://en.wikipedia.org/wiki/Capital_gains_tax#Singapore

[sses]

Yes but they won't be US taxes, which are the only taxes US immigration law cares about in this context. He's still avoiding US taxes.