I see that he hasn't snooped into Chrome at least, can never be too sure about the rest of the hard drive.
If I would want to read someone's files without them knowing about it, I would create an image of the entire drive. This can easily be done by booting a Linux LIVE OS, or by temporarily plugging the drive into another computer. You wouldn't see any of this on your file system.
Or buy a hardware cloner, clone the drives and read them later.
Put client disk in slot 1 blank disk in slot 2 & push a button. Drink beer. Then put disk back in client PC.
PCs / phones / tablets. We live our life on them now, and even the paranoid people can't remember everything that they may have accidentally stored on one.
-Dave