I disagree, but let's consider what this shows us. Nothing was out of place in the area with the guns. Only the knife was. We didn't even notice a missing gun like last week.

So that would mean that the killer used a gun they got from the machine, or they have had the gun in their possession since before this. However, they took the time to place the knife.

So that means we either have two people, or we could have one very skilled criminal trying to give an impression of being irrational so it would point towards someone less experienced. If there are two people, then we have to figure out who used the knife since that would be the person deemed guilty per the rules.