Case Full Metal Jacket:
People have been found dead with 'metal' shards 'sprayed' into them.
Someone invents a new weapon and thinks he can hide his murders as supernatural events.
Some creature is hunting people, but not for food.
Something that was once human is taking revenge or retribution for something .
Useful lines of inquiry:
The relations between the people
The relations between the time of the attacks
The relations between the location of the attacks
The search for a witness to any of the attacks
*The nature of the 'not metal' that the people were killed with