German prosecutors allege that Wirecard AG executives overpaid for a string of companies, causing massive losses to shareholders of the now disgraced financial-technology company.

Playing a key role in some of the Wirecard deals was Henry O’Sullivan, a behind-the-scenes payments consultant who was paid as an adviser on at least 10 separate Wirecard acquisitions, according to former senior company officials. The acquisitions he advised on were among a larger group of deals done at inflated values, the officials said. His paid role on the deals, not previously reported, builds out a picture of what investigators say was a key aspect of the company’s collapse.