edit: mass downvote! here are the links.
this link talks specifically about signal protocol being used by organized crime https://www.volkskrant.nl/nieuws-achtergrond/waarom-criminel...
https://www.securityweek.com/telegram-rivaling-tor-home-crim...
https://nakedsecurity.sophos.com/2019/05/03/criminals-are-hi...
https://www.independent.co.uk/life-style/gadgets-and-tech/ne...