 He held a valid firearms certificate , allowing him to possess a single semi @-@ automatic weapon . He used this weapon at approved gun clubs for sports shooting at targets . His erratic behaviour , including shooting at dummies dressed in wigs , and modifying his bullets to make them more powerful , led to him being expelled from one club , in Telford , Shropshire . His nickname there had been " The Cowboy " . Members of another gun club where Williams was a member had expressed concerns that he was stealing bullets . 
