From where do you assertain that he still owes the tax? Perhaps the IRS says he still owes the tax, but he's been to court and won. How will they go about getting the tax now? They have tried him in Federal Court and lost. Did the judge rule that he owes the tax? If not I don't see your point.
The avoidance of criminal charges does not let him off the hook. The tax liability is still due, he just doesn’t get free room and board for the next 10 years.
See 141 for the success rate for these scumbags.