No need to apologize- I have probably done my fair share of confusing you in return
What I was trying to ask was if you have tried to match evidence such as the fingerprints to all the other prints you have collected [to rule them out], the same with all the DNA samples. Even though you have matched them to something already, a thorough CSI would compare them to all the other samples even though he/she knows they will not match.
There also might be some questions you have left over- with the student and the webmaster [those two are the most often missed by other players], or there might be things you needed to look at [but not collect- eg. newspaper clippings or the book at the webmaster's home] that you might have missed looking at. Doing those things might get you to 100%.
I doubt that because the game is second hand that that would impede you from getting 100%- getting the 100% in Garvey's Beat [in particular] is aggravating in both the XBOX and PC versions of the game because the story line is fairly easy [no real twist or surprise], so it's very easy to miss some "little thing" which costs you the extra percentages.
Have you finished the other cases? If not, I would suggest taking break from this case and come back to again later with fresh eyes