the problem for terror investigators: too many to watch

The colossal challenge confronting authorities trying to prevent and track an attack like the one in Paris is that there are too many people to watch.

With continued immigration and their high birth rate, the Muslim population of France reached an estimated 6.5 million in 2013. Although French law prohibits collecting official statistics about the race or religion of its citizens, this estimate is based on the average of several recent studies that attempt to calculate the number of people in France whose origins are from Muslim majority countries.

This estimate would imply that the Muslim population of France is now approximately 10% of the country's total population of around 66 million. In real terms, France has the largest Muslim population in the European Union.

Of these, only an estimated 5,000 are now under some form of direct observation or surveillance by French security services because of their involvement in various jihadist movements. Those 5,000 are just the cases that French authorities know about.

Many officials suspect there are many others who are radicalized in some fashion, but have not made it onto the radar in France.

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