Yup, but our issue is we need to find the bad guys center of gravity and disrupt it. Okay, this guy was know to the Brits. Great, but in Western society you need more than an indication, you need evidence. It's one of the beautiful things that separates us from the radical Islamic terrorists and strongmen like Putin.
So, we have to get to these people before they are radicalized. That is their weak point, their center of gravity. Otherwise, they'll be radicalizing people for years to come and we won't be able to stop every car, truck, or knife attack. Nor will we be able to stop someone from making a very powerful but crude bomb. Believe me, it's very easy to do and it can be done with everyday items.