That’s the whole point. It narrows the pool of suspects. While the owners have every right to refuse, the cops also have every right to ask for voluntary co-operation.
For myself, I’m conflicted about what I would do if placed in this situation. You want to see a killer brought to justice, but why should owning a gun make you a suspect?
Would you be “conflicted” if you were the parents of one of those kids?
What if:
-Someone stole my gun, used it for the killing, and put it back in my car?
-Bullets fired from my gun are ‘identical enough’?
-What if the evidence gets mixed up and I fry because of it?
-What if the a detective thinks I did it, and messes with the evidence?
Here’s a GREAT video about why you should never talk to the cops by a University professor. There is a part II as well:
http://www.youtube.com/watch?v=i8z7NC5sgik&feature=related