Washington ? The Internal Revenue Service is failing to ensure that tax evaders pay their back taxes and penalties, allowing convicted scofflaws to routinely ignore their criminal sentences, a Treasury investigation has found.

The report of the Treasury Inspector General for Tax Administration, to be made public this week, found that of 172 tax convictions studied, more than $2.5 million in back taxes, interest and penalties went unpaid by people who ignored their sentences.

For example, the IRS’s criminal investigations division closed 37 cases with probationary periods ending from 2000 to 2002. Of those 37, only six complied with their sentences, which included payment of back taxes, penalties and interest, the report said.