When Sian O’Callaghan went missing on March 2011, CCTV evidence quickly led police to taxi driver Christopher Halliwell.
They arrested him on suspicion of kidnap, with Detective Fulcher believing Sian may still be alive — and that Halliwell was their only hope of finding her.
With this in mind, Fulcher made the decision to interrogate him not at the station, but in an isolated countryside spot without a solicitor present. Halliwell confessed to murder and led him not just to Sian’s body, but to that of Becky Godden-Edwards, reported missing four years earlier.
Watch it on ITV.