The reason Byron got arrested is because he didn't call the police after he shot the teens. He waited in his basement, shot Nick as he came down the stairs, shot him again when he was prone, dragged his body into the garage, waited 10 minutes, shot Hailey as she came down the stairs, shot her again when she was prone, and dragged her body into the garage. He then sat in his basement rambling to himself about how he had to kill them, which he recorded, He only called his friend and told him about it the next day as 2 bodies rotted in his garage. He claimed he "didn't want to bother the police on Thanksgiving". His friend then called the police. The jury said the recording was the main reason they believed it was murder.
So, he basically dug his own grave. He could have shot Nick once, called the cops, the teens would have went to prison, and he would be free.