A spring morning at Columbine High School, Colorado, 1999. By the afternoon, 12 of its schoolchildren and one teacher lay dead, gunned down by two of its pupils.
Cases such as Columbine are occurring with increasing regularity and guns are not always involved. In Japan in 1998, a 13-year old schoolboy murdered his teacher in a frenzied knife attack - one of the many similar crimes that has shocked that country. In Britain street crime has escalated beyond our worst fears, and teenagers account for a large proportion of violent robberies in their desperation to steal must-have items like mobile phones and sports clothes.
Crime expert Antonio Mendoza investigates this world-wide problem and comes up with some shocking findings.
