Read on Twitter
Lots of stuff about the Reading suspect being "on the radar" of the UK's security services. This is how I understand the situation:
1) His name came to the attention of the Security Service, MI5, in 2019. The information suggested he might be thinking of travelling. That, in their world, means potentially travelling to take part in terrorism or related activity.
2) Now in any given week, there may be 100s of such "leads". A lead is something that needs to be looked at - but is not an investigation. Something that needs to go into a triage. We don't know what the information was that MI5 learnt or how detailed it was.
3) If a lead is really detailed and can be corroborated (ie information on an identifiable individual with compelling information about their plans) its prioritised depending on the urgency of the threat the individual poses (this process is all in the public domain, by the way)
4) But if a lead can't be developed, it's dumped. Hypothetical example - anonymous call to police says a bloke called "Bill" down the market is planning a far-right attack. Who's Bill? Which market? It's not really a great deal to go on.
5) Some leads can be developed - but then dry up. This may be the case here. The information was looked at but the suspect was not found to cross the threshold to be investigated. So it could be that he had said he wanted to travel - but there was no proof he wanted to fight.
6) And so, the suspect did not become a target for investigation - what's known as a Subject of Interest - because, at the time, there was nothing to justify chucking resources at him.
I have no doubt more will come out about this at inquests into these terrible deaths. In the meantime, read this piece I did some time ago about how difficult I personally found it when I tried to make these judgement calls: https://www.bbc.co.uk/news/uk-48839789
