Marijuana smell in apartment complex

[Kaitlyn Seigfried]

There has been complaints of the smell of marijuana on the third floor of my apartment building. It's actually only one person that has notified me of the smell, but she has multiple times. I have no idea the unit it is coming from. However, the tenant doing the complaining has a problem with one of our other tenants on the floor and she is accusing that tenant of being the culprit. I've sent out a threatening letter to the whole building that once we find out who it is they will be evicted, but that hasn't stopped it happening because how do we prove it's them. The complaints obviously happen after hours. My question is do I have the tenant doing the complaining call the police the next time they smell the marijuana? They are looking to us as the landlords to do something, but we have no proof of who is causing the smell.