He was found guilty of first degree murder, which requires a showing of a premeditated intent to kill. The premeditation does not have to consist of lengthy planning, but instead proof of a considered thought process and knowing, intentional action designed to kill or inflict grievous bodily harm. Premeditation can occur in a matter of minutes.
His bringing a knife (!) to a track meet itself shows premeditation, as did the litany of evidence about the killer saying, "Touch me and find out." Compare that to coming home and finding your wife in bed with another man, you are enraged and shoot one or both. No premeditation there - you just went into the house, zero plan on inflicting harm. That would be 2nd degree at most, likely manslaughter.
