Due diligence is more than just "show me some bank statements"
Yeah, it's fraud, but it seems like there wasn't enough DD from investors who got mugged off.
Faking a bank statement would be almost trivial these days, so shouldn't enough to tick the DD box. But the banks aren't going to just hand over confidential account information, balances, deposits etc. to just anyone who asks, so how does one verify?
I still think the investors should have dug a bit deeper, instead of seeing a unicorn and going through 3 (three!!) funding rounds before pulling the plug.