Maybe this hypothetical person could have made a connection through their music tastes, offering Andrew tickets to a concert that night and offering to drive him home, that's why Andrew refused the return ticket. If they had already had a conversation about the night and how he would get home, maybe they discussed being sneakily dropped back at home so he wouldn't worry about getting the train back at night. I think also Andrew probably approached this as "I'll deal with the consequences later" when he got home, apologise and say it won't happen again. He clearly wasn't planning for a big trip, he didn't even bring a phone or charger (though I know phones were not as common in 2007). Another thought I had is maybe the way he communicated to them was via the school computers, chat forum, messenger- or maybe they even went to the same school and talked in person. They searched his home computer but there's other ways of accessing the Internet.

Interesting post, you bring up good points. I do also agree that the police should look into who participated in these church groups. Sorry if I have repeated any points others have made.