By the end of the 1970s, about 1,500 police forces had sent officers to New York to learn from Bolz’s practical experience of more than 200 hostage incidents. These lessons travelled even further when a BBC documentary crew sat in on a masterclass delivered by Bolz and Schlossberg, a former traffic cop with a doctorate in psychology. For Schlossberg, Stockholm Syndrome – or Survival Identification Syndrome – was not a complicated concept.  

“We simply mean when two or more people get together, they form a relationship –  that’s all it is,” he said. “Of course, the more stress in the situation, the quicker the relationship, and the more intense it’s going to be. When people are in crisis, and they’re not sure about what’s going…