Armchair detective is a term used for a fictional investigator who does not personally visit a crime scene or interview witnesses; instead, he or she either reads the story of the crime in a newspaper, or has it recounted to him by another person. As the armchair detective never sees any of the investigation, the reader can attempt to solve the mystery on the same terms as the detective
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Do you know anyone that hasn’t been shocked or disturbed? Has anyone you know had an unusual or inexplicable reaction? Was their behaviour unusual on the weekend of December 17 to 19, or in the past three weeks? Do you know someone who has been behaving out of character either by actions, or what is said – or not said? Do you know someone who has inexplicably become reclusive, quiet or vocal?
http://www.bbc.co.uk/news/uk-england-bristol-12212365