Oh indeed, Dante. They hoover up so much info these days that it's pointless, because they don't have the ability to sort it or make heads or tails of it until they are directed to look at it specifically. I completely agree.
In this particular case, I was thinking more about someone they were already specifically after, and using even low tech tools like comparing ink in the letters, or in past cases that I've heard of, collecting the DNA from licked stamps and things like that. There are many non-hi-tech and non-internet tools at their disposal as well, and sometimes they only create a trail when used together, which can be difficult for even a very smart perp to plan ahead for. That's all I was intending to say.