Even State Department-funded Human Rights Watch admits that authorities combine legal and illegal methods to obtain convictions: https://text.hrw.org/report/2018/01/09/dark-side/secret-origins-evidence-us-criminal-cases
Combining dragnet surveillance with device hacking is intended in the design of both tools. Hence, State Department-funded Signal dupes you into handing over your identity as part of the population-centric mapping. In custody, your phone will be hacked when it is taken away if it’s important.
https://xcancel.com/hannahcrileyy/status/2034273723667161480#m
Relevant xkcd.
If someone is already a suspect of something and they have the social network graphs of them they can cross the information and put others in the watchlist. Enough suspects interacting with each other can lead to a more thorough investigation and extract information by other means, it’s not like things like ICE cares for human’s right.