It's a little different when a jury of your peers convicts you of a crime which was democratically passed by a legislature, versus a lone gunman who feels he is the judge, jury, and executioner.
So expressing the sentiment that nothiong excuses murder and still having a death row is just I congruent and wrong.
And yes, both the will of the people and tradition can justify capital punishment.
But then again, the society apparently defines the quality of a killing - only future history will tell if this is a murder, and thst can go back and forth a lot depending on public sentiment.