MIAMI AP – A federal judge refused Monday to postpone prison or consider a lighter sentence for a former Swiss banker-turned-informant who helped launch a massive U.S. tax evasion investigation into banking giant UBS AG.

The decision by U.S. District Judge William Zloch means Bradley Birkenfeld must report to prison Friday to begin a sentence of three years and four months, which is longer than what prosecutors had sought. Zloch also refused to schedule a hearing on whether to reconsider the sentence. Birkenfeld pleaded guilty last year to a fraud conspiracy charge.