I agree. They know which train he took and when it arrived at King's Cross. They knew which clothing he was wearing and bag he took.
I disagree a bit.
The parents were the ones telling the police Andrew had left and came back from school to place the uniform in the washer. The parents located the CCTV footage from this neighbor’s cam and determined this was Andrew leaving the house (there’s no publicly available footage of Andrew coming back dressed in his uniform, we can’t know what’s a confirmed fact or an assumption). And the parents approached and talked to the ticket seller on Monday.
There’s no CCTV record of the Doncaster train station or the ATM where Andrew supposedly withdrew some money. There’s no independent witness of Andrew leaving the home in his uniform that morning apart from a church friend from the family. So, literally, without the King’s Cross footage,
this would be the only possible recorded piece of evidence in this case (again, as far as we know). There’s no way to confirm this was indeed Andrew unless you had cameras in the other blocks as well to establish the path this boy took (i.e. if this camera is on block B, a camera on block A could capture this same boy walking around a minute before when ‘Andrew’ was supposed to be in the family home, also in block B).
So, the King’s Cross is – objectively – the only piece to sustain the narrative Andrew went to London. Again,
based on this (the neighbor's CCTV cam), there's no way the family could say Andrew was wearing a Slipknot T-shirt. There's no recorded testimony of the family saying so in those early days to the police. And if they did, I'd find it downright suspicious: ask any parent of a teenager to go over their wardrobe and tell you exactly what T-shirt is missing from there.
I'm not saying I don't think Andrew went to London. I'm saying that the narrative itself is only supported, independently, by this King's Cross footage. The police were working with the hypo he could have gone to London, but they couldn't know what train he took, or if he took a train at all in those early days. There's a version of these events that could simply be boiled down to a misidentification of the images. Like 'Jaz' being Amy Bradley.