I realized that I'm pretty sure it was Ezra who nabbed Shana and left her at the edge of town in her car with the spray paint on the sign saying "don't come back." He'd been researching them for a while and earlier in that episode we see him looking at the photos on his computer from that day. When he looks at the ones of Shana it seems like he looks more concerned than when he's looking at the other girls. Then when they're in NY he gets there so fast and knows Shana is the shooter. I'm guessing he figured out that she was up to no good much earlier. He nabbed her like that as a way to try to scare her into leaving town and leaving the girls alone. He probly had a hunch she was gonna do something but didn't know for sure. That's why he already knows it's her in the NY episode.

Also I noticed some people talk about how creepy he is in the scene where Mona goes up to talk to him out on the street and he starts saying stuff to her about fear being the number one motivator, and how Mona looks so scared (like hes so creepy he even scared her). Well I realized that scene wasn't what people seem to think it was about. He wasn't just being creepy for no reason. Mona had just learned that he was writing the book and wanted him to stop bc he had alot of dirt on her. She approached him and starts by casually mentioning Aria and how the girls get so much attention from him (this got his attention). They then go sit and talk and if you listen to what she says you can see shes actually trying to threaten him. She says stuff about how he knows all about living a double life. She's trying to threaten him into stopping his book by making it clear that she knows what hes doing and will out him. Thats when he starts talking about fear and how she learned to get rid of her fear. He says it can be a good thing but it's also bad because it makes her underestimate people and with fear she would know how far she can push people before they push back. He's talking about himself. He knows shes trying to threaten him and he's saying that she's underestimated him and that if she keeps pushing him he will push back (reveal her secrets). Thats why she looks so scared after. Because she's realized she can't threaten him into ending the book and telling all her bad deeds and that if she keeps trying then he'll just tell them sooner. A couple episodes later he calls her into his classroom to talk and she gets this little smirk. It's bc she's realized he changed his mind and is ready to negotiate. She realized she's not going to be completely screwed by the release of his book anymore.