[f3llowtraveler]

He wouldn't owe any taxes. At least, not any income tax. The coins were worthless when he first mined them, and so there wouldn't have been any tax due.

If he were to sell the coins now, he might incur a capital gains tax, depending on where he lives.

[xiphias]

The tax fraud doesn't have anything to do with Bitcoin. The top comment explains it more, but it was clear from earlier news about him as well.