HI
Just echoing what Dangerzone posted- you can combine the paint can partial print with the glass prints in the same way you got the glass prints together- just be sure to use the prints themselves, not the can. Drag the partial print (first evidence tab) onto the combined glass prints (first evidence tab) to combine all the prints together.
When you put the glass prints together in the first place, you could have either put the pieces of glass together [therefore making the prints on them join] or the partial prints together. Most people put the glass pieces together. Sadly can't do the same with the spray paint can- you have to use the partial print itself.
... methinks I should add this spiel to the walkthrough to make it clearer