Another scenario, Google constantly runs a system looking at tweets, texts, and news stories. Anytime something happens that is criminal and significant enough

Another scenario, Google constantly runs a system looking at tweets, texts, and news stories. Anytime something happens that is criminal and significant enough for it to notice, it turns up the logging for all the Glass devices in the area. If it were opt-in to send the resulting log to law enforcement, that would be totally fine. If not, things get worrisome. But what about in between? Say sending the log in is only done when the user clicks ok, but the police subpena Google for who all had their Glass devices in that area, so they can contact them directly. Gets into the area of withholding evidence and such.