Who ever it is, needs to be found and everyone who abused it should get an appropriate punishment... e.g. kept on killing for their achievement should get an appropriate ban and excuses oh well its not mine and I kept on killing them should not count, at no point this should count in anyone's mind legit...
Just to be clear, I dont say everyone who killed one of them needs to be banned, but anyone with lets say more than 100kills should be counted as exploiting the game in unfair way...