FWIW, the part about not buying a return ticket never struck me as suggestive because I constantly do the same thing myself, even in situations where I need a return ticket. First because our train ticketing system is so fiendishly complicated (day returns, open returns, off-peak returns, off-off-peak returns, returns only valid on routes going via Hull, whatever). Second because like many people I practice conversations in my head first and if the other person goes 'off script', my default is just to automatically blurt out no or no thank you, without even processing what the other person said.
In terms of Andrew using the internet, it does seem highly unlikely but it can't be conclusively ruled out. I'm a little confused by the posts confusing "using the Internet" and "having a website." Most people don't have their own websites the way the Columbine shooters did. When I was in my early teens I was completely obsessed with a particular TV show so used to go to an Internet cafe occasionally to visit fansites and fanforums for that show. My internet activity would have been 100% untraceable unless a eyewitness had come forward to say I was at the Internet cafe at a specific day and time, or if someone somehow made the connection between my real life identity and the username I used to post with. I'm not suggesting this as a realistic possibility, just saying it can't be 100% ruled out.
I'm English, and respectfully, I completely disagree with this. Or at least it doesn't chime with my experience or the experience of anyone else I know who went to school here in England. I was in school around the same time as Andrew and bullying was totally ignored.