A new documentary, Sarah Everard: The Search for Justice, examines how police tracked down the man that was later convicted of her murder.
In this clip, investigating officer DCI Katherine Goodwin recalls the moment she was told that their suspect, Wayne Couzens, was a serving police officer.
Viewers in the UK can watch the documentary on BBC One, 21:00GMT, Tuesday 5 March, and on iPlayer here after broadcast.
