I think one of the Russian oligarchs is still in prison after falling out with Putin. Im assuming he made his money in a semi-legal manner.
I was gonna mention Pablo Escobar. He built his own damn prison/resort. But I guess he falls afoul of the legally acquired wealth rule.
Nice assumption!
Does brief imprisonment prior to being beheaded qualify? Henry Stafford, Duke of Buckingham, who turned against King Richard III—possibly after being ordered to kill the Princes in the Tower—was a multi-billionaire in today’s money Also a multi-billionaire was Richard FitzAlan, Earl of Arundel and Surrey, who was imprisoned and beheaded for treason against King Richard II.