They're not that smart. There's been several cases of "secure phone systems" getting breached by the govt who then got access the entire underworld's communications.

Why don't they just use Telegram / Whatsapp / Signal? Sure maybe the NSA can get in but afaik they don't bother with mid scale European cocaine importers.

Am I wrong in thinking that you could bypass Signal / E2E security by having access to the display (screenshots)? Is that a lot less feasible than access to the microphone or camera? Maybe that's much harder at the OS level?

No, they won't. Also, define criminals. Plenty of crimes are done by people who are not professional criminals who spend money and time on opsec.

We’re talking classic bandits that wear eye masks and striped shirts. REAL professionals who’ll stuff all their treasures into a big burlap sack with a dollar sign on it.

I doubt those use smart phones.

s/criminals/protesters there fixed it for you