Useless: "Tracking" Islamic Assassins

So, what's the point of "knowing" and "tracking" these Islamo-fascist killers if we don't do anything with the information?

London Bridge Attacker Inspired by U.S. Based Islamist Hate Preacher

Brietbart, 8 Jun 2017

"A friend who had reported London attacker Khuram Butt to anti-terror police said the 27-year-old killer “used to listen to a lot of Musa Jibril.” He added: “I have heard some of this stuff and it’s very radical. I am surprised this stuff is still on YouTube and is easily accessible.”
"[A] study by the International Centre for the Study of Radicalisation (ICSR) found that 60 percent of surveyed foreign fighters in Iraq and Syria followed Jibril on Twitter."

And yet, in 2015:

 U.S. online ban of militant Muslim preacher ends

Reuters, Tue Apr 7, 2015

"A [Dearborn] Michigan-based Islamist preacher whose online sermons have been a leading source of inspiration for foreign fighters in Syria is free to return to social media after restrictions on his Internet use lapsed."
http://www.reuters.com/article/us-usa-religion-imam-idUSKBN0MY2CP20150407