And I sent home a questionnaire, asking their parents because most of the children in the class come from other countries. In fact, just about everybody in America comes from another country if you trace far enough.
Offenders were far harder to trace than ever before, he added, since they were now communicating through the internet and social media, rather than by phone, and sometimes leaving "no footprint".
While police have so far found no trace of Ms Rushworth, who disappeared in June 2009, body parts belonging to the other two women have been found in the River Aire in Bradford.
