Actually it did not - SoftBank employees contributed into a special purpose fund created for this investment, and that fund bought a convertible bond issued by Wirecard.
Although it has been reported as a "SoftBank investment", it's pretty clear that no SoftBank money was part of the deal.
That's almost worse. The fact that SoftBank employees were willing to pile their own money into this fraud should tell you something about the due diligence they're doing when dealing with other people's money.
I don't think you're aware of all the details here. The special purpose vehicle also structured a transaction with Credit Suisse which effectively allowed the bonds to be resold immediately to institutional investors. The fund (i.e. SoftBank employees) had no ongoing risk exposure and pocketed the pre/post-deal spread in the share price.
Although it has been reported as a "SoftBank investment", it's pretty clear that no SoftBank money was part of the deal.