Minnesota authorities are using contact tracing apps to arrest protestors

Thanks so much for that observation. The tweet doesn't say "contact tracing apps", it says "contact tracing." Those might be entirely different things!

I'm still interested in how exactly they're doing it, but it might be as simple as asking the arrested people, running background checks on them, or digging through their phones and possessions.

Came to say this. This is likely a misunderstanding of the tweet, which I don't consider very trustworthy to begin with (people all over twitter are calling bull on "Every single person we arrested last night, I'm told, was from out of state").

Regardless, you should assume that that data can and will be used in a court of law if some bright, tech savvy detective has the brilliant idea to do so. The fact that a certain bunch of id's was encountered by the contact tracing app on your phone (because obviously they have access to the data on other arrestee's phones) will greatly strengthen their eventual case against you.

Frankly, it's an investigator's dream tool. This is why I was never in favor of the measure in the first place. Without an extreme level of discipline from investigators, there is no guarantee they won't use the tool. Furthermore, given what we know of parallel construction as a technique, we're already in waters where we can't even say that there's a good chance it isn't being misused, but having it's misuse covered up.