Londoners today marked the third anniversary of the July 7th London bombings that killed 52 people. The city's surveillance cameras helped catch some of the terrorists responsible for the attack.  Many U.S. cities are now installing more security cameras. But critics warn that increased surveillance violate individual privacy rights. Leta Hong Fincher has more.

Londoners laid wreaths outside the King's Cross station Monday to remember the bus and subway passengers killed in bomb attacks three years ago.

Surveillance cameras helped identify the terrorists responsible for the killings. Peter Clarke led the anti-terror police team.  "We have identified CCTV footage showing the four men," Clarke said.

Researchers find that Britain now has more than four million surveillance cameras and one study says it is the most monitored of all Western industrialized states.

Some cities in the United States are catching up.

Security cameras in Phoenix, Arizona recently caught airport workers stealing from checked bags.

Several years ago, a surveillance camera in Florida showed a man abducting 11-year-old Carlie Brucia. The man was later convicted of her murder.

Washington D.C. city officials say they are setting up what will be one of the world's most comprehensive, centrally controlled visual surveillance systems. More than 5,000 cameras track the movements of citizens in an effort to fight crime.

U.S. civil libertarians say increased surveillance in the society is reminiscent of George Orwell, who wrote in his novel 1984 that "Big Brother is watching."

Barry Steinhardt of the American Civil Liberties Union says, "There is no other system in the U.S. that has that kind of extensive network of cameras."

Washington City Administrator Dan Tangherlini says the cameras improve safety.

"We can't let the genie back in the bottle, we just have to figure out how to manage it and control it,? he said. 

Law enforcement officials say that surveillance cameras help catch criminals and are here to stay.