Tenant damaged lock; no one claims responsibility
I inherited four tenants on 4plex, rented the attic as an art studio. 3 units share a common entrance.
This morning I get a text from one saying a key is broken in the lock and it doesn't open/unlock.
I went there and replaced the lock, provided new keys to two of the tenants there (who didn't have a broken key) and so using elimination, figured it was the 3rd tenant.
Texted the tenant and they claim their key works fine and they didn't break anything.
Because I can't prove who did it, assuming all 3 return non-broken keys (and for two of them I don't know what their key looked like before hand i.e. style/coloring etc) do I just eat it or is there another way to determine who the culprit is?