X, Y and Z mutually decided to beat up A. One evening, they gathered near a secluded area through which A passed every evening while returning home after work. X and Z followed A from a distance whereas Y was waiting with hockey sticks a little further. Suddenly, X attacked A from behind, casting blows on him. Z, on the other hand, blew a whistle indicating Y to come with the hockey sticks. Upon Y’s arrival, X and Y started beating up A severely whereas Z stood by the side watching the fight. In the meantime, A’s eyes fell on a knife lying nearby. He picked up the knife and ran it through Y’s chest. In a state of confusion, Z rushed towards Y, picking up a hockey stick. However, A thinking that Z was about to attack him lifted the knife and inflicted grievous hurt on Z in the process.

Keeping in mind the aforementioned facts, determine the criminal liability, if any, of X, Y, Z and A. In each case, substantiate your answer with sufficient reason and case law wherever required.     (20 Marks)