How much have you been following this case? Police have said, and still maintain that there is no evidence that anyone knew him personally in any kind of intimate, friendship or otherwise type of relationship. But that doesn't mean he didn't know who they were, and watched and followed (stalked) them. Everything points to that, nothing points to a direct relationship with him by anyone in the crime house, or anyone the victims knew in their social circle.
Maybe that could change after the go through all his electronic devices, but I'm betting all the victim's electronic devices have already been analyzed and I'd think if there was any connection at all it, some evidence showing that would have been found on some of the victim's phones, etc.