Footage from surveillance cameras along the Boston Marathon route gave the FBI early clues about the bombing suspects. And prosecutors say they'll use some of those images to try to prove their criminal case against 19-year-old Dzhokhar Tsarnaev. But the proliferation of cameras in America's big cities is raising some tricky questions about the balance between security and privacy.

It was pictures of two brothers taken by a camera outside the Lord & Taylor department store that provided the first glimpse of the men who allegedly bombed the Boston Marathon.