| DutchRits |
I had the key locked up in the office safe so they got it early on. The big deal is probably the hidden storage aspect, the lock should probably be able to be broken with a crowbar. Something Lorrimor's (or many PCs') tools could into but not a rampaging escaped prisoner.
Storywise I said they kept the high emotional attachment murderer's tools so that if the prisoners escaped they could scry them down.
The Safe's opening DC is equal to the Property Room's doors in (S16). I can see forcing the physical solution of prying it open, but my point was that unless you brute-forced the Property Room door or had an ungodly Disable Device check, you weren't going to get access to the 5 Prisoner's Items until most likely just before you engage TSM.
I definitely was worried my PCs would ask why the weapons were kept in the secret vault, particularly when NONE of the other prisoner's valuables in (S16) were detailed. I took a similar approach to yours; they could be used to scry upon the prisoner, should they escape. I also included the clothing each prisoner wore upon arrival; per the module text, they were stripped at their Induction, and it stands to reason that their belongings would be cleaned prior to being folded and stored in the Property Room until their...release.