This is do log in plugin folder with all the players did (put lava / fire / TNT) and let the server admins in chat as the player X put in place X TNT / lava / fire.
There are too many of these plugins to count, just goto plugins.bukkit.org and search for Anti grief or something
I used this plugin http://forums.bukkit.org/threads/sec-info-griefalert-v1-9-know-who-is-griefing-1337.33507/ and do. Thank you.