I think in the physical space there's a lot of ways investigators can discover this information after the fact, whether it be interviewing witnesses, looking fo

I think in the physical space there's a lot of ways investigators can discover this information after the fact, whether it be interviewing witnesses, looking for forensic evidence (fingerprints, DNA), etc. Things that, arguably, are not privacy violating, but can be acquired in investigating a specific problem. The difference in the digital space is that Twitter/Facebook/etc. have all that forensic data... and then just refuse to provide it.