File a grief report following this format : http://www.ecocitycraft.com/forum/viewtopic.php?f=59&t=11587
Unless he witnessed the griefing himself, the only way to be sure is to file a grief report and have a supermod determine who grieved.
You are right I was wondering if a mayor himself can check who has been griefing. It seems quite tedious to always have to bother the supermods in order to find out who griefed so that you can ban the right person. You would not want to ban the wrong persons, however still you would like to act fast and correct.
