Have you ever thought he was arrested for a reason. If the cops had ignored what he did and left him free, some would demand he be prosecuted. By arresting him, (perhaps even telling him what to say in interview) no one can moan. Sometimes it helps to think 'out of the box', there is often a good reason why something happens.
Going back to the 2 welsh lads, if they had any nouse they would have departed the scene once the lad was arrested. If i was the cop i would say thanks and tell them to buger off qucik, that way they cannot be identified and cannot be hounded by the far l*ft of this country who demand 'justice for all.'