Echoes of the attack that left 22 dead and 59 others injured in Manchester, England, made it all the way across the Atlantic.
Within minutes of the attack at Manchester Arena, New York City police dispatched heavy weapons teams to high-profile locations like Madison Square Garden. In the Dallas area, police also made a show of force at a John Legend concert, CBS News' justice and homeland security correspondent Jeff Pegues reports.
The bombing at the Ariana Grande concert exposed the outside of arenas as potential "soft targets."
"The goal, obviously for these folks, 'I don't have to hurt everyone. I just have to make my mark,'" said Ron Hosko, a former assistant director of the FBI.
Hosko says terrorists view people entering and exiting events ranging from papal masses to hockey games as easy targets. Security is typically relaxed when an event ends.
The Manchester attack shows that security teams may need to rethink strategy for when events come to an end.
"Rethink: 'How do we push security,' and we've seen this at airports as well, how do we push those security perimeters back in a way that just doesn't make the choke point further back?" he said.
But in some places it's not practical to change the perimeters.
It's especially challenging in Times Square, where 300,000-500,000 people pass through a pedestrian plaza on any given day, CBS News correspondent Don Dahler reports.
With eight streets and multiple sidewalks converging there, it's a vulnerable area that police say they simply can't make 100 percent safe.
Police acknowledge that they can't do it alone and that there is strength in numbers. In New York, subway posters encourage people to watch for danger.
Police say tips have stopped violent attacks. The FBI has said most terror attacks in the U.S. could have been stopped -- if only someone had reported suspicious activity.
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