The perp knew?
For all we know, he didn't even know who MB was, or care, when he broke into the church that night.
There's no objective reason to say perp even knew MB would be there. Or a class. Or that he knew there was any info on FB somewhere mentioning a schedule. Or that he had any sense of who would arrive when, or who would arrive first, and so on. Or that he cared about any of that.
What happened later doesn't tell us what he knew or intended, and until we figure out who he is, we can't answer those questions.
While we can start with the assumption those things are true, it's just an assumption without an objective basis, and all of them instead could be wrong.
I find it informative that LE has gone back and forth on whether or not this attack was planned. Obviously they started out looking closely at the ones who might have known MB and have a motive, because that's the ones easiest to find and examine. But from their statement and actions, that has yielded nothing, leaving them the much broader group of people who didn't know her. That seems to tell us what the evidence shows so far (or fails to show).