Again let's go through some facts here. Somebody wrote that Katie's house is very close, in the other direction, from the crosswalk. And considering she turned the other direction at the crosswalk, away from her house, she would probably be at least half an hour late getting home. She did not inform her girlfriend that she just saw, that she would be late getting home. She did not text her girlfriend during the walk, that she would be late getting home. She was not even seen going through the camera at Charles Allen gate. Instead she walked at least partially the way, through a closed park, in the middle of the night, by herself. To get to this destination.
Only one explanation really makes sense. And in my opinion, she was meeting somebody there at the bathroom at the Charles Allen Gate at 12:30. And possibly this person even told her, do not tell anybody I'm meeting you, especially not your girlfriend, and do not go through the gate because you will be on camera, walk on the park path instead. I believe there was going to be a short business transaction there. And then Katie was going to leave and go home. Possibly texting her girlfriend after the transaction.
I believe this was a pre-planned meeting. But there was no communication by phone or text. To hide evidence of this meeting. She was possibly walking around for a long time that night, hoping to run into him earlier. But she didn't. So she stuck with the plan to go over there at 12:30. And the perp carried out his plan. He lured her to that destination. It was his attempt to terrorize a whole city.
Edit- So if my theory is correct, who is the perp? Let's speculate. Well he is somebody who appears non-threatening. Because he is somebody that Katie did not have any problem with, meeting alone in a park late night. She trusted him. He is somebody that would come into contact, thru her world, possibly of music and the midtown bar scene. He's probably somebody that knows her girlfriend too, on at least a casual level. So he probably goes to those bars in those areas fairly often. But he probably also does not know her too well, or he would come up more on the radar. And there would also be some text messages and calls to the guy. He's probably not some crazed ogre looking guy. He's probably not too young or too old, and probably closer to her age.
He's probably also someone who has the ability to sell a certain product, which I will not mention here. And there could be a story behind that too.