Intentionally killing someone without lawful justification is by definition, both legally and morally, murder. Planning to do the same is capital murder.
Morality and legality are not always the same thing in this country.You may vigorously disagree but I firmly believe that there are many things in this country that are legal but immoral as well as things that are moral but illegal.I've never been a juror but if I were I would always take the moral path over the legal one in cases where the two paths were in conflict.
If this kid's account is accurate then IMO the moral path is to,very probably,convict him of negligent homicide despite the possibility that Texas law would require me to vote guilty of "murder".
It's clear that many here disagree...but I'm willing to be in the minority on this.