How did they manage to do so spectacularly badly? I think part of the problem is that they were trying to predict times and locations, rather than focusing on individual offenders. Past record is highly predicitive of future behaviour, i.e. if an offender has committed assault half a dozen times, it is highly probable that they will commit another assault or similar violent offence again, we just dont know when or where. Poor quality data may also be part of it - garbage in, garbage out