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If you saw something suspicious, would you say something?

If something suspicious happened right in front of you, how would you react? Rossen Reports stages a revealing hidden camera experiment.
/ Source: TODAY

The brothers responsible for the Boston Marathon bombing in 2013 planted backpacks in the crowd. Last May, a terrorist reportedly used a backpack in the attack that killed 22 people at an Ariana Grande concert in Manchester, England. And just last year in New Jersey, two men found a backpack on a suburban street that turned out to contain a bomb.

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We've all seen the signs and heard the pleas from law enforcement: "If you see something, say something" has become a national slogan. From airports to bus stations, movie theaters to parks, authorities ask the public to report anything suspicious. But if something suspicious happened right in front of you, would you notice? How would you react?

With the help of local police and a group of volunteers who thought they were there for a general story about public parks, TODAY national investigative correspondent Jeff Rossen and the Rossen Reports team staged an experiment in a park in suburban New Jersey. Hidden cameras recorded what happened when a Rossen producer dropped a backpack on the ground and walked away, and the results were revealing.

Police say there are many red flags you should report, not just backpacks: someone dressed oddly for the place or weather; people taking pictures of bridges, tunnels, or airports, or someone looking the opposite way than everyone else or walking a different direction than the crowd.

A Rossen Reports producer drops a backpack near a crowd in a hidden camera experiment.TODAY

The best idea in such cases, police say: Call 911 immediately. For more information on how to report suspicious activity, visit the Department of Homeland Security's "If You See Something, Say Something" page.

To suggest a topic for an upcoming investigation, visit the Rossen Reports Facebook page.