There is definitely more here, sounds like it could be very compelling case. DA is not going to show all the cards right now. I'm guessing there's info that either establish the shooter was so homicidal that not securing a gun is just criminally negligent (invol manslaughter) or that the actually knew about the plans and they are potential actual accessories. Flight is indicia of guilt. Expect a defense of a bully who threatened the shooter, and constitutionalizing defense (2nd amendment, right to own, no law or duty to store in any particular manner)