His social presentation — charming, well-groomed, described as intelligent — was largely at odds with a pattern of killing that emerged in the late 1960s and left investigators suspecting him in far more deaths than he was ever convicted of. The confirmed murders were carried out with improvised weapons and followed by deliberate efforts to mislead police, suggesting a practical, unsentimental approach to violence. His time in prison became a minor scandal in the Netherlands, and his eventual release after a life sentence drew continued public and journalistic attention that followed him until his death.

As the architect and administrator of the NDH's concentration camp network, he held direct authority over the conditions and operations that resulted in the deaths of approximately 100,000 people at Jasenovac alone. His role extended beyond administration — he personally directed early mass killings in the field and remained the effective authority over the camps even while nominally under house arrest. The combination of organizational control and direct participation in atrocity made him a central figure in the Ustaše genocide against Serbs, Jews, and Roma during the war years.