I recommend this short article Digital Smoke (pdf) by Al Lewis of Paradigm Solutions. Mr. Lewis has accurately characterized the problems facing not only police agencies, but also users (and defendants), and lawyers as they deal with allegations of computer crimes or internet crimes.
About the user, Mr. Lewis writes:
Today?s computer users can be characterized by the following: they have computers that are more powerful than the computers used to put a man on the moon, they have no computer security training, they use 3-4 applications, have multiple computing devices, freely publish personal information through a wide variety of data repositories using technologies they do not understand, and are connected to the Internet via a high speed connection. In essence today?s computer users are easy targets.
Given this lack of understanding on the part of the user, and the general lack of training on the part of first police responders with respect to computers and other devices, valuable evidence can be lost, altered, or tampered with, which can lead to wrongful accusations and convictions.