Yeah, you’re talking about unknown/not-yet terrorists, but I expect that people that have actually committed terrorist acts in the past to be either behind bars or reformed (spending 20-25 years behind bars may make you change your mind about killing inocent people the next time). By definition, people that have not yet committed any terrorist acts are not, well, terrorists, thinking otherwise risks making us dive into thought-crime territory.

When such people is in 100m range from event - nothing can be done

Police forces _has_ to act before such happens

This is like metal detectors in airports - useless

Coz if someone want to do harm - they can do this on parking, in line or in any areas near where people are crowded

And even more There is no evidence that facial recognition lower terrorists attack possibility

Members of terrorist cells do. However they’re not terrorists until the actual act of terrorism.