Mike Fagel, professor at Northwestern University and Homeland Security contractor, talked about the threat of retaliation and travel concerns.
Security is being increased at major cities across the country following President Obama's announcement about the death of Osama bin Laden.
New York City plans to dispatch more officers to airports, bridges and the World Trade Center. Los Angeles officials say they're increasing intelligence monitoring, and Philadelphia plans hourly checks on mosques and synagogues.
Though the Chicago Police Department told NBC Chicago this morning the Windy City is not on heightened alert, the Chicago Office of Emergency Management and Communications (OEMC) said public safety personnel are monitoring the city's surveillance cameras and maintaining "a visible presence to protect residents and visitors."
The OEMC made it clear there are no known terrorist threats for Chicago, though a number of precautions are being taken.
Mike Fagel, a terrorism expert and Northwestern professor, said it's not uncommon for a city to avoid alarming its residents. "We should be very cognizant of potentials," Fagel said on NBC 5 Monday morning. "We don't want to alarm the public inadvertently and say things that may scare them into being paralyzed."
The cities that confirmed efforts to increase security probably aren't the only places taking extra precautions, Fagel said. "It's very likely the entire nation will experience a much higher degree of alertness over the next 24 to 48 hours."
Should the United States be worried about al Qaeda? Fagel, also a contractor with Homeland Security, said various terrorist groups on the fringe might be a bigger concern.
But that doesn't mean Americans should stop traveling or avoid large buildings.
"People should remain vigilant, as we've suggested all along," he said. "We have a tremendously valuable transportation administration, police force, Homeland Security. Everybody is doing all the things they really can do."
"Don't panic, enjoy life."