> In the universe of a competent FBI, which I think is ours, they already know who is in the network.

Certainly they know the handles of those people, and what they've said and what documents they've exchanged.

Connecting Signal accounts to real-world identity... well, that's definitely the FBI's wheelhouse, but some might make it easier or harder than others.

But there are a few cases where even the Internet sleuths are pretty confident about identity.

> So why does (if the press is to be believed) an authoritarian, fascist, ultra-right-wing regime allow them to operate?

Rationality requires treating behaviour inconsistent with a quality as evidence against that quality.