Eric would definitely pull something like TJ Lane did with his "Killer" shirt. I can only see him showing no remorse for his actions and being very proud of what he did. Like verbatim, he would definitely be defiant and rowdy in court, likely would be held for contempt and argue with whoever he felt was insulting him or attacking his superiority complex. I doubt he'd pay attention to any victim impact statements or testimonies and would try to provoke the victims/family of those murdered for fun. I really don't see him acting even remotely civil for more than an hour.
Dylan, I can visualize he'd act like Payton Gendron. He would just own up to his actions and plead guilty with no second thought. He would most likely only speak when spoken to, act very reclusive and provide a half-assed apology statement to the victims. I expect he would write very dramatic & out of pocket shit in his prison journal shortly before killing himself in his cell, too.
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A wreck-devoted seaman thus might pray to the deaf sea