A user by the name of atomlib just admitted to griefing, though I’m not sure what he griefed exactly.
Here’s a screenshot:
http://i.imgur.com/iB2Wt5i.jpg
And the transcript:
<atomlib> does this server have block log plugin?
<IRBMe> I think so, yes
<atomlib> oups
<atomlib> I'm leaving now then
<atomlib> sorry about griefed stuff
<IRBMe> What did you grief?
<atomlib> everything
<IRBMe> At spawn?
atomlib left the game
He was at coordinates x = 359, z = 644 when typing. I had a quick look there after he left, and it seemed to be buildings belonging to a player called dwarvenmines, or something like that. It didn’t look like much was damaged, though there were a few blocks missing, and it looks like some of the wood was on fire.
A mod might want to check out that area, or if possible, have a look at what atomlib touched.