I'm a bit torn on this. Of course a 13-year-old is capable of committing a great sin and a great crime, but there is a sense in which they're still immature. I think that their youth should be taken into account as an exenuating circuмstance when it comes time for sentencing. I don't believe that a 13-year-old should be subject to a death penalty, nor do I believe they should serve time in an adult prison system (due what would inevitably happen to them there). Perhaps something like a life sentence with a possibility of parole after about 10-15 years, depending on whether they show any clear signs of rehabilitation.