Why giant airports are hard to secure

How do you completely secure something as large and rambling as an international airport against a terrorist violence like the one on Monday at Domodedovo Airport in Moscow? You cannot, security experts I spoke with on Monday say.

Airports are by definition public places requiring comparatively free access. The experts have long contended that serious holes in security at airports have been ignored while most of the endeavor and money goes into looking for weapons on passengers at checkpoints. But they have also warned that an amazing event in one place can direct to widespread overreaction and demands for quick fixes.

Douglas R Laird, a past Secret Service agent and onetime head of security for Northwest Airlines who now operates an aviation security consulting firm, Laird & Associates, made much the same case.