I think it's obvious that the real culprit here is the fact that he was forced to catch the school bus at 6 AM in the morning. No jury will convict him, once they find that out.
Allowing the death penalty on a case by case basis for people who are not yet 18 is consistent with other parts of our society. On an individual basis, some minors can become emancipated and acquire many of the same rights and responsibilities of someone older then they are.
As long as the process of determining eligibility to die examines the accused and doesn't focus on the crime itself, I think this will fit our current definition of justice. That said, I remain uncomfortable with the number of people executed and later found innocent. Even one is too many. As our science progresses, our standard of evidence for execution should increase too. If our technology and justice system cannot deliver a slam dunk, then the person should be locked up.