I'm trying to construct some of these confirmed facts here into coherent arguments for both sides but they seem to still go both ways. You could say: see, he was spurned, he must have plotted this murder for days. But, he was visibly nonchalant at the concert and didn't arose anyone's concern. And he was with some other girl . . . I almost wonder, based on the OK Cupid profile, the other girl at SFTW, if he had a few little internet girlfriends.
It also seems like Emma was being cruel to him on the ride home. But, why did it take him so long to do it, if he planned it out? What was the significance of that night, the 15th, as opposed to the 14th? The 16th? Presumably, he would have had similar opportunities. They certainly slept on the 14th.