Val McDermid's book "Forensics" is a good collection of anecdotes about how it's done. She includes the case of Suzanne Pilley, murdered by her lover David Gilroy in 2010 - the conviction was only possible because of mobile phone records, which were good enough even back then. But the records weren't quite good enough to reveal exactly where he buried her and the body still hasn't been found.

Gilroy was a regular customer at the charity bookshop I worked at. He had really boring tastes - contemporary fiction of the sort that gets to the middle of the best-seller lists and nobody remembers a few years later.