Lack of any kind of police work by the cops

I do not understand why they did not first run ballistics on the bullet. Find out what type of gun was used. Find out which of the suspects had access to that type gun and test the dads gun for having recently been fired. If he says yes you can test it...then they know who did it. If he says no...because he knows his daughter is guilty it should at least send up a red flag. Instead they grab circumstantial evidence of a wallet that could have been put there by anyone since it was outside and ran with it. Was this filmed in Keystone?