As someone who has been on the receiving end of federal seizure orders for cryptocurrency private keys, they were in my case satisfied by publishing a transfer (signature) to a USG address, not actual disclosure of private key material, despite that being explicitly stated in the order.

This indicates a level of US Fed LEO technical sophistication I’m somewhat pleased to hear exists.

I have heard that they have been developing an in-house technical capability and department for this since at least the time period of the Ulbrich arrest and the "first" Silk Road.

Either that or they just approached it like a bank account and simply wanted the money and didn’t care about the cryptographic specifics whatsoever.

More likely their work with an outside consultant/firm.

What's a USG address?

USG =US Govt.

It's not an either/or thing though, right? IMHO, it seems plausible for the FBI to get a private key from a cooperating exchange?

To the previous poster's point: it didn't say which private key. There can be multiple with cloud storage.

From the press release, the scare quotes could mean anything, but they likely had the rough equivalent part:

for which the FBI has the “private key,” or the rough equivalent of a password needed to access assets accessible from the specific Bitcoin address.

Did the crackers surrendered the private keys? And if so why was a warrant issued?

https://www.elliptic.co/hs-fs/hubfs/Screenshot%202021-06-07%...