Mostly there are zero suspects. These subpoenas are, as you point out, ways to find more suspects. There's just one issue: they also often only turn up ONE susp

Mostly there are zero suspects. These subpoenas are, as you point out, ways to find more suspects. There's just one issue: they also often only turn up ONE suspect. And here's the thing with people and police: everybody lies. The victim of the crime lies. Suspects lie (but the thing is: suspects lie whether or not they've committed a crime, this is not a difference between innocent and guilty). Witnesses lie (don't want to get caught, and yes the police encourages this, at wrong parking. Police will encourage them to lie, because they can't ignore a confession of wrongful parking and they understand they'll lose cooperation if they write them a ticket for their trouble). And of course the police officers themselves lie. Whatever hope you have of finding the underlying truth in such a haystack less than a few years of work ... forget it. And then comes Google with "concrete evidence". Something that is actually true. Very likely not related to the crime, but true. So you can probably understand that this would introduce quite a big bias against a "suspect", when their real connection to the crime is "someone was shot, and this guy googled 'gun' 2 days before". Furthermore, this gives them something to put to a judge or a jury, when before they had nothing, or nothing coherent. Do you really think at this point a police officer, judged by the number of cases solved, bad guys put away, just walks away without at least applying very strong pressure on whoever was fingered ?