Couldn't help this one.
So he committed a murder,and he is a minor, and you want to know if the police were wrong for questioning him without a lawyer present?
Maybe he should have thought of that aspect, called his attorney before the police arrived on scene.
I have NO, sympathy for your son, nor you for not even thinking of the poor soul your son killed.
I love my son, but I would be the first to recognize a problem with him before he wasted his life, and that is what your son just did.
There is really no advice to give you, and you need to live with that.