International tax evasion, state purchases of confidential bank data and voluntary disclosures

International tax evasion is a major source of discontent for tax authorities worldwide. State purchases of whistleblower bank data on suspected tax evaders from international tax havens is a potentially powerful policy tool tax authorities may use unilaterally to combat such tax evasion. Tax authorities in North-Rhine Westphalia (NRW), Germany’s most populous federal state, have been the most active internationally in acquiring such confidential bank data in the first half of the 2010s. Using unique self-compiled press data on the timing and content of altogether 10 data acquisitions from Switzerland, a major offshore financial center and tax haven, and on monthly voluntary disclosures of international tax evasion involving Swiss banks, we study the response of voluntary disclosures to news of such acquisitions in the period 2010–2015. Our results show that media reports on new purchases of whistleblower data had a positive, immediate and sizeable effect on the number of voluntary disclosures filed. Various robustness checks and additional explorations corroborate this finding. For NRW, these purchases generated additional tax revenue of more than half a billion euros.