“You were the seventh Horcrux, Harry, the Horcrux he never meant to make. He had rendered his soul so unstable that it broke apart when he committed those acts of unspeakable evil, the murder of your parents, the attempted killing of a child. But what escaped from that room was even less than he knew. He left more than his body behind. He left part of himself latched to you, the would–be victim who had survived."
Harry Potter: The Deathly Hallows (part 7), page 592
Murder alone doesn't create a Horcrux it takes intent. This section of the book states that Harry is a Horcrux even though not intended. JKR latter said he isn't officially a Horcrux but considering it is stated that this incident is what caused Harry to be considered like one then why didn't the death of James also fracture Voldemorts soul into a third shard that would have flung off to attach itself to someone or something. There were two murders and a third attempted which should have caused three splits of the soul. Now even though he didn't intend for a Horcrux to be made two were made Harry and the piece that Quirell found. Why isn't there another? This nicely constructive para added by Kevin on my request to clarify the point...
OK, so Voldy can't kill both James and Lily with one single spell.
He must have killed James first, then aimed at Harry when Lily came in between.
The reverse can't be true, because the moment he had killed Lily, he would have been destroyed!
So, when he killed James, his soul should have split, or am I missing something?
Why didn't his soul split?