Examining one of the most baffling unexplained deaths of recent years. In August 2010, Gareth Williams, a GCHQ employee on a 3-year secondment to MI6, was found dead inside a padlocked duffle bag in the bath of his London flat.

Susanna Reid looks at how one of Britain's most cunning serial killers John Cooper was finally caught after 20 years with the help of his appearance on the game show Bullseye.