That's simply not the nature of a LE or intelligence bureaucracy!
Analysis of recordings of license plates, analysis of DNA - to identify some young people who have raised a white flag on a bridge.
Well, then maybe I should remind you about the ridiculously low success rate of London's Metro police stop and searches of civilians:
The Metropolitan Police used section 44 of the Terrorism Act more than 170,000 times in 2008 to stop people in London.That compares to almost 72,000 anti-terror stop and searches carried out in the previous year. The Met said anti-terror searches had been more widely used since the planting of two car bombs in central London in July 2007.
Of all the stops last year, only 65 led to arrests for terror offences, a success rate of just 0.035%.
The dates are so old because I wrote about this in 2009 already. There's a huge welath of such examples in the Western world. The stop and search thing is no "intelligence collecting power", but I suppose you get the point:
Don't lead LE or intelligence agencies into temptation, for they will not resist. Limit their powers, and punish transgressions ruthlessly!