You're missing the part where, for that to work, we have a government with access to a massive surveillance system capable of identifying and tracking the population at scale.
And you're missing that, instead of specifically identifying a specific individual doing a specific thing, this network would be used to place under suspicion, investigation and possible arrest, people who's only documented action was "being somewhere."
Oh, and while your example is "committed a crime", that same network could easily be used to identity and track people who were, say, coming and going from protests. Or libraries. Or voting.