Chicken eating egg.

I have a chicken who in front of my very eyes devoured an egg. Just built a bolt on run and this one particular chicken came out got very excited and it was almost as if it were in shock dropped an egg whilst drinking and it almost startled it as it spun round 180 and pecked it, cracked it and then within seconds all 5 were at it before I had a chance to rescue it.

That was a couple of days ago and nothings happened since, however this morning there appeared to be an egg shell which I am not sure if it was a shell brought up from the previous episode or the culprit has struck again although there were 4 other eggs next to the remains, so why just the one I do not know.

I can't raise the nest box, so what options are available to me? Do I do the fake egg trick? Do I blow an egg through and fill with mustard in the hope of the culprit doing it again and getting a dislike for eggs? Any help most appreciated.