None of that has anything to do with the evidence against him. There is no evidence of a weapon of any kind in the kids' vehicle. Unless they find gun residue on the deceased kid's hands, Dunn is toast.
He left the scene. He finds out the police are looking for him and he leaves town. He drove 170 miles away. And it's 4 days later and he still hasn't called the police. They had to track him down from video at the gas station.
This is not the horse you want to attach your wagon to.
What is this "gun residue" that you are refering to?