On: If this type of dark matter existed, people would ...

[tomatotomato37]

Presumably odd angles of entry would also be a clue. A shot that enters near verically while the victim was standing would be extremely unusual in a one-story building if you aren't expecting the "bullet" to have come from space

[pure-awesome → tomatotomato37]

Also, wouldn't there be a tunnel all the way from the top of the building and through the person?

People would wonder if a government agency wasn't using some sort of drone or satellite weapon to eliminate targets.