He certainly didn't know everything, but he knew a little bit about the vampire in town. He agreed with Dean that Eric should be dead already, but he could only assume that there were reasons that Dean hadn't ganked him already.
"Maybe we just need to hunt him down," he said, as if it were that simple.
Perhaps it was, but more than likely it wasn't. The guy seemed to have a following of sorts and hunting him down might mean biting off more than even they could chew. At least when it came to being in a confined space like the City. All the same, Sam wasn't one to shy away from a fight and if Dean needed him, he'd be there. That was just how they worked.