Instead, the lights and sirens heard in Center City on Wednesday morning were part of a emergency drill conducted by the Philadelphia Police Department's Homeland Security Unit.
Dozens of Philadelphia police officers were called to a staging area on JFK Boulevard in Center City.
It was a 'rapid deployment' exercise. Homeland Security officials decided that, in light of the killing of Osama bin Laden, it would be smart to make sure they were prepared.
"If there was a terrorist attack, and it occurred in Center City, we would define what the crisis point is, what our parameters are, what our perimeters would be," said Chief Inspector Joe Sullivan.
About 50 officers were dispatched, briefed, and given their assignments before being sent out to different parts of Center City.
"The officers don't know when we're going to call them down, but certainly know when we're going to do these drills so we can deploy people across the city without stripping any district of its resources," said Police Commissioner Charles Ramsey.
Ramsey said there have been no terrorist threats to any U.S. cities, but he believes his officers - along with those who live and work here - need to be on guard.
"I've been in touch with the Homeland Security Department and the FBI," Ramsey said. "Philadelphia and every city needs to have a level of preparedness."