One that's ignored here is the one of the Manchester Canal serial killer. The death rate along the canal is far higher than anywhere else in the country (the last count I saw was >70, but there have been a few more since), with the majority of deaths all fitting a similar profile (young, male and been separated from friends), yet every one is dismissed as an accident by the police quite quickly.
It's just very unusual. Too many people are dying along the canal for it to be normal.