Kristil Krug told police in Broomfield, Colorado, that she and her husband, Dan Krug, were receiving threatening texts and emails from an ex-boyfriend. Two months later she was dead, but her alleged stalker had an alibi.

Now, on the 50th anniversary of her killer's arrest, those closest to the case have shared their stories as part of BBC Sounds series The Cop, The Kidnap and The Killer. The series follows the journey of Det Ch Supt Robert Booth, of West Mercia Police, who led the investigation into the kidnapping.