I would issue it ASAP with a written verification from the witness as the previous poster said. We had tenants two weeks after they moved smoking in the apartment. There is no smoking on the property per the lease. The smell was seeping into my home. Two family home. Repeated verbal & written notices were given to no avail. It was only when my lawyer sent a letter threatening with eviction that it stopped.
Be prepared for them to deny it. My tenants tried to deny it until one of them locked themselves out. When I opened the door the smell of smoke almost knocked me over. Needless to say their lease expires next month and is not be renewed. Good riddance!