Police Superintendent Randall Halstead says the man was stopped Tuesday by an officer who saw him acting suspiciously. He says the man dropped the backpack.
Halstead says the man also faces charges of disturbing the peace and disorderly conduct.
The backpack was blown up by the bomb squad as a precaution as was a second unattended backpack found nearby. Halstead won't say what was in the second backpack or who owned it. He says police are investigating.
The backpacks rattled nerves on the anniversary of the Boston Marathon bombing, which two pressure cooker bombs in backpacks killed three people.