The tenth level of the Tate Modern has a viewing balcony where visitors can take in scenic views of the city. It was also a place to pick up some refreshments. Children with endless energy and enthusiasm ran around. Not many people took notice of the 17-year-old loitering. Later, when CCTV footage was analysed, it was evident that he had trailed behind some children, intermittently peering over the railings, seemingly to look at the hard concrete, ten floors below.…