She showed them a pack with one cigarette missing.

BBC: Airport evacuation smoker acquitted

The Levinson family says Robert was working as a private investigator looking into cigarette smuggling in Iran when he went missing.

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The samples could come from the personal items of the missing -- from toothbrushes and hairbrushes to used Kleenex or cigarette butts -- or by using a cotton swab to rub the inside of a survivor's cheek.

CNN: Somber Manhattan back at work