How It Works
After busting open the toolbox, teams found 19 pens, as we said.
Only one of four letters in "Papermate" were ever blacked out on the pens, M-A-T-E. This was both a clue to grouping the pens and also a hint for the next step. "Mate", along with the strange font on the Gumshoe Unlimited Brand Toolbox label, both suggest a method for creating letters from the pens. By mating the colored tape in each group and sorting the result by M->A->T->E, you get the following:
Notice the extra pen. This 19th pen has tape on it, but none of the letters in "Papermate" are blacked out. Since you've already opened the toolbox and you still haven't received a combination for the lock, the only thing left that's possible open is the odd-pen-out.
What's this? A strip of paper concealed within the pen! What does it say?
Well, that's not very useful. But what happens if we wrap it around the pen we just opened?
Ah ha! Instructions for opening the lock. Without further ado:
What's this in the lock? A tiny piece of paper:
Carefully unrolling it, what does it say?
And there you have it, the solution to the puzzle, ABRACADABRA.