You can't just throw the person out.but you need to give them a written notice. Then you must file for an eviction at the district court. Then it will take up to 30 days to have them removed . Even with just a verbal agreement you are still renting the space, so that gives them renters rights. Now if they are only just staying there and they do not receive mail there , I believe that this comes under the trespassing act , but I'm not sure on that one . What I would do is contact the local police and ask them if they can help you out . But most likely they will tell you that you have to take them to court . If they have threatened you ,you can file for a pfa with the police then the will come and escort them out of the building . Don't ever rent to someone without a lease , even if its only a month to month lease.good luck
