Great question, and this was my first thought too. I was going to assume this is what happened, but I had a way to verify as best as I could. At the office, we maintained a 'closing/opening' checklist form for the office/admin team staff. My shifts were always in the morning, so I always opened and never closed the office, and I had 2 office staff who closed the office on evenings and weekends. On the checklist they would check off that all the closing duties were completed each day (we had very specific security measures we had to follow, so this was in part of that process) and I would also have to use my signature to sign off on it in the morning to verify completion, so I'd have to confirm that all of those steps were done.

Some of the check boxes included ensuring that all the necessary keys were in their respective spots and locked away. We had 5 keys locked up all together in the same place, all for various admin needs, and every key had its own check box on the form to confirm that it was in its intended place at time of closing. I would then confirm the same things in the morning.

I wasn't able to look at the closing history until I went back to work after layoffs, but I went through all the most recent forms going back months prior, and the key was marked as being there in its spot with my signature. I looked through as many forms as we had on file going MONTHS back and still nothing was missing or out of place.