Open ending

When Sydney saw that his son had a seizure and was in pain,he dind't know what to do.Kill him or not...he already had the pillow in his hands.Sydeny thought that his son was suffering and finally he killed him.The same way like Earl Detraux did.If Shawn hadn't had a seizure at this moment when his father was with him,he wouldn't have killed him.Sidney didn't know that his son wasn't suffering during his seizures,it was a great feeling for him of freedom for his son.