[nineinchal]

Even if they were legit, shouldn't there have been some effort to repay by son?

My take on this is that the son received $30 M in income and never paid tax. Also, no interest income was recognized by the father on any of the returns. No gift tax was paid.

At some point in time, the nature of the loans became a gift, even if there were legit notes. The son can never hope to repay that money.