Paris Attacks How Great Are the Terror Dangers Posed by Refugees?

It has now been confirmed that one of the Paris suicide bombers reached Europe disguised as a refugee. Security officials had long felt that such a scenario was unlikely. How big is the risk?
A photo of the Syrian passport found near one of the suicide bombers in Paris, as seen on the front page of the Syrian magazine Blic on Nov. 15.

A photo of the Syrian passport found near one of the suicide bombers in Paris, as seen on the front page of the Syrian magazine Blic on Nov. 15.

ANDREJ ISAKOVIC/ AFP
Photo Gallery: Anger and Sadness in Paris
Christopher Furlong/ Getty Images
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Photo Gallery: Anger and Sadness in Paris