MADELEINE BRAND, host: And those random searches of bags and packages in the subway prompted our      colleagues at the online magazine slate.com to ask if this kind of      screening is indeed legal.  Slate's Daniel Engber has this Explainer.</s>DANIEL ENGBER reporting: The searches can be legal, but it depends on how they're done.  The      Fourth Amendment protects people from unreasonable searches or seizures.      That means that as a general rule the government can't search your      baggage without a reason to believe you're a criminal.  But according to      legal precedent, a random search is acceptable if it fulfills a special      need, like public safety. If New York subway screenings were challenged      in court, the city's lawyers could argue that the program's primary      purpose is to protect the city from terrorism.</s>DANIEL ENGBER reporting: Let's assume the courts believe the subway searches are an effective      deterrent for terrorism and that the recent subway bombings in London      make them reasonable.  Then a judge would have to consider whether the      scope and duration of the searches is appropriate.</s>DANIEL ENGBER reporting: The first random subway screenings occurred last summer in Boston during      the Democratic Convention.  A district court ruled that searches on      trains that ran beneath the convention center were acceptable since they      took place in a restricted area for a limited amount of time.  The New      York City searches, though, are taking place all over the system and seem      to be of open-ended duration.</s>DANIEL ENGBER reporting: The judge must also consider how individuals are selected for screening.      If police officers have too much discretion, they might single out      certain kinds of people for what are supposed to be random searches.  To      prevent profiling, cops are sometimes given a strict formula.  In Boston,      for example, every 11th passenger was pulled aside at some commuter rail      stations.  The New York Police Department says it's using numerical      criteria, but spokesmen also say that large or suspicious-looking bags      can be red flags.</s>MADELEINE BRAND, host: And that Explainer from Slate's Daniel Engber.</s>MADELEINE BRAND, host: Stay with us on DAY TO DAY from NPR News.
Slate contributor Daniel Engber explains the legality of random searches of riders on U.S. subways.