It is difficult to gain any useful information on file modifications without knowing details on what files were modified, and if they were actually modified rather than accessed.
Some files and/or programs will have a change in access dates just when a computer boots up. There are programs that index the hard drive and/or scan for virus infections that would change the access dates, but not the contents.
Oh, and I am an IT guy, and I have been using Internet Explorer since 1988. I sometimes use FireFox, but IE is my primary browser and has been since Netscape Navigator kept crashing at version 2.11. :seeya:
ETA: IF the CPD were trying to tamper with the computer to make BC look guilty, they did a REALLY poor job of it. Why not change the system date and time, then fire up Google and search for stuff like "Strangulation 101", "Spouse Killing for Dummies", "All I needed to know about Murder I Learned in Kindergarten"? That would leave a far better trail, IMO.