This is worse than I thought. The FBI says only 64% of the murders in
the US lead to an arrest and they don't actually get a conviction on
all of them.
Here is a story on NPR. That should be a liberal enough source for you
lefties.
http://www.npr.org/2015/03/30/395069137/open-cases-why-one-third-of-murders-in-america-go-unresolved
So two-thirds lead to an arrest. The third that does not means it's not
worth trying in your mind? Strange logic.