Roman, I still cant work out why would you not talk to Kisiel directly at the party. This bit makes me/us confused and suspicious. I understand and appreciate the fact that you use your personal time to organize the event but thats not where the problem is. You did not tell anybody about this at the party, Kisiel found out when he got back home - this bit just makes no sense. If I see damage to my equipment I raise voice at the time or the moment I find out not 2 days later.
Anyway I think it makes no sense to discuss this further as its not going anywhere. If thats what you guys decided and you are 100% sure the damage was made by Kisiel then fair enough - ban him, I personally think its very unlikely that Kisiel did it deliberately - Also I see no reason in you accusing innocent person but again the issue should have been solved at the party place with everyone around not after the party.