“The most disturbing facet of this ubiquitous childhood disorder is an utter lack of empathy,” Mateo said. “These people—if you can even call them that—deliberately violate every social norm without ever pausing to consider how their selfish behavior might affect others. It’s as if they have no concept of anyone but themselves.”

“The depths of depravity that these tiny psychopaths are capable of reaching are really quite chilling,” Mateo added.

Late in 2007, Gerry McCann gave an interview to an American magazine and talked about the decision to publicise the eye defect. “Certainly we thought it was possible that [the publicity] could possibly hurt her or her abductor might do something to her eye . . . But in terms of marketing, it was a good ploy.”

It is this unsettling mix – of the incredibly intimate and the coolly tactical – that has made the mystery of Madeleine McCann arguably the biggest and most extraordinary child abduction story in history…