"We're in a heightened state of preparedness everyday. We can't afford to be reactive and go to a heightened state," said Chief Inspector Joseph Sullivan.
Extra uniformed and undercover police have been deployed since Monday's bombings. They are keeping a close eye on the city's historic attractions, transportation hubs and vital infrastructure.
The fear is that the Boston suspects may have been part of a network.
Now that they've been identified, law enforcement will quickly get a clear picture of who they've been associating with.
"Every shred of information that comes in, they compare that with their databases of known suspects in Philadelphia to ensure there is no connection. At this point there has been no connection made," said Chief Sullivan.
If there is a threat, Chief Sullivan says the city is prepared for a massive deployment of forces, much like what has been seen in Boston.
The Joint Terror Task Force and Homeland Security teams in the surrounding counties have trained together and share the same equipment and technology.
The suspects may have been part of a network, or they may have acted alone.
Al Qaeda has been aggressively using social media and the internet to recruit and train homegrown terrorists in the United States.
Congressman Pat Meehan is on the Homeland Security Committee. He says we can all learn from what happened in Boston.
"Unfortunately it's a harsh lesson in that we are never really completely safe. In a dangerous and radical world, these things can happen abroad and unfortunately happen here too," said Congressman Meehan.
Meanwhile several large and high profile events are coming up in the months ahead in Philadelphia. The City is promising extra tight security, some of it highly visible, but much of it, undercover and behind the scenes.