Human rights v Human wrongs

A common thread emerges from the atrocities seen in recent times.
The perpetrators are not necessarily immigrant, but more often than not, home-grown and already known to police, intelligence services or medics. They will have more than just a "chip on their shoulder" against the society they despise, wish to have their say,  one final word, cry of outrage and act of violence.
Someone somewhere, frequently will have sufficient knowledge of such a potential terrorist, and be in a position to flag up the need for intervention.
From this premise; all persons known to police, intelligence authorities and the like, might be required to complete a written or online psychometric test, crafted in such a way so as to reveal any propensity to act out violent thoughts.  Belated police claims of having had someone "on the radar" quite unsatisfactory, insufficient, and not good enough.  Innocuous questions can elicit the sort of responce peculiar to a certain type of person, and a person in a disturbed frame of mind will be quickly found by computer algorithm, given the right set of queries.
A way of preventing someone from achieving their perceived "moment of glory" would doubtless be greeted by human rights activists with the shout: "foul play".  However, in times such as these, there are better causes to fight for than the freedom to commit acts of potentially lethal violence.  One way terrorists reveal themselves is online; by the searches they make and sites visited, much can be deduced and is the principal way "police radar" becomes alerted. Deeper surveillance targeted here is surely not beyond those charged with keeping public order. 

The usefulness of psychometric testing is well recognised in selection of persons for employment and routinely forms part of military selection, including pilots for example. I took one, aged 22, as part of an entry test for a flying competition held in 1966 by the Woodbine Tobacco Co.  I answered questions published in the Western Morning News  that seemed to have very little relevance. Answered casually, posted off the form, and was astonished to later find I had been selected to take part, and subsequently gained a PPL. ( Flightglobal Report ).

Further indications of psychometric testing usefulnes:  Here BBC