To give more info.
My friends situation is that they have no idea how much money they owe, the IRS does not know about this money because it's simply potential taxes owed during anonymous crypto trades, maybe.
Apart from that, his friend should be taxed for the trades made.
OP, what you comment has already been discussed in other threads, and it is not a rare situation. There were people who got Bitcoin when it was worth little and now find they have a large capital.
I already commented that it is preferable to act before the capital becomes very large because when it is already large and you have no way to prove where it comes from you run into a problem, and the solutions are two:
1) Pay lawyers and tax advisors to help you to legalize it, which will have high costs and you cannot trust 100% that you are not going to have problems with the justice.
2) Go to another crypto-friendly country, which also has costs. It also has emotional implications.