Langbar International

We know that Arad and Menzel knew each other from DIA.
Why did Menzel walk away from this? - did he think they were pushing their luck? - did he offer some sort of PN/CD that Regli/Rybak wouldn't accept?

Menzel met Rybak through Rybaks daughter. It may yet be shown that Rybak was innocent at the start - Arad needed a frontman to run the business, and, at the time Rybak fitted the bill from his IDS experiences, as later Stuart Pearson would fit the bill.
Maybe Rybak found out about the scam and was able to negotiate the founder shares based on keeping quiet. This could also be why Menzel walked away - if Rybak confronted him over this.

As for Regli, what does he gain?...he isn't making £££ from this. OK, he gets paid, but it's not the millions that Arad/Rybak can make.
Would Regli, as Treasurer then CFO, have seen the CDs? - more than likely.
Would he open the BdB account? - why wouldn't he?
So how would genuine CDs be replaced with fakes?

This may yet come back to Arad and a corrupt BdB official.

I certainly hope Menzel is also being hauled in for questioning.