I’ve had the same thing happen with Citi. No warning, just woke up and found mine and my wife’s accounts frozen pending closure. I’m sure heads will roll when they realize who they’ve upset, but as for me I never found out.
By US law you can’t tell the customer that you’re closing their account because you thought it was “suspicious.” You just do it and then submit a Suspicious Activity Report (SAR) to FinCEN.
I can see how a high net worth individual could have account activity that looks like money laundering, but given his long history with the bank would be surprised if this decision was made automatically or by some junior analyst. It must have been escalated to someone senior, and they must have known who he was and still made the decision.