Then the officer will ask him how did he get the fund to purchase the share at first place. Unless the share he bought only worth penny, and come to the time he sold it worth billion. Then it will be deemed as capital gain and he is temporary safe. But regulator can then narrow down scope to investigate on how this penny stock company can grow to billion when he sold the share. Layer by layer to be drilled down.

The question is source of his wealth, if it is from his father, then his father need to show how did he get such vast amount of wealth, and it has to be legitimate with proper tax filling and tax payment records to show how he can have 2 billion in his lifetime. Like his set up business 1980, and has been making almost 100 million profit and pay 24% tax every year since 1990, and paid out remaining profit as dividend to him over these years, then it will be legitimate source of income and no issue at all