User blog comment:IPFreely/SamHain Question/@comment-1509826-20130530235456

Indeed, it was the Witch Don Stark, who was a follower of Samhain, what he was chanting was the spell to summon Samhain from hell, which required a third blood sacrifice for it to occur. He intended to sacrifice his sister, and fellow witch Tracy, so that he could reap the rewards when his master arrived, however as Sam and Dean killed him, he ended up being the third sacrifice.