I'm pretty sure we'd all agree Voldermort killed Lily and James because they wouldn't reveal to him the recipe for their multi-award winning pumpkin pie. Hmmmm, pumpkin pie.
Little does Voldermort know the actual recipe if encoded in nanobots living in Harry's scar, and will play a crucial part in the Dark Lords downfall.... Hahahahahahahah. How silly this all is.