Lack of 'rigour'-mortis

Hmm, it seems pathologists can't find the reason how the code-breaking British 'spy' Gareth Williams, found stuffed in a bag in Pimlico, died. Well, why don't they just put bronchial pneumonia on the death certificate. That's the normal thing they do in a post-mortem when they can't work out/can't be bothered to ascertain the method of expiration.