"Known to the security services".
Every. Fucking. Time.
I was genuinely waiting to see if this would turn out to be the case in this attack and- sure enough- it was.
And yet- as the OP observed- they can, and will, use this as an excuse for a blanket crackdown on civil liberties- just as they've tried following every "known to the security services" attack- despite the fact it wouldn't have helped here.