Here is the screenshot of the griefer admitting.
The guys name is PizzaGun.He asked me to join my fac nicely and after he joined he built a super noob house.
I told him to rebuilt a nice home or he will be kicked then he started griefing and the rest of the incident is clear in screenshots in above link.
I hope he will get ip ban too.
george_2004 said he also reported him for griefing.