Royal Air Force Puma helicopter is pictured flying over the 2012 Olympic Stadium during a training flight over London on Aug. 18, 2011. Britain will have 13,500 troops deployed on land, at sea and in the skies to help protect the London Games. Typhoon fighter jets, helicopters and two warships will all be on duty to guard against security threats. (AP Photo/SAC Phil Major RAF, MOD)

Police officers take part in a search exercise, June 19, 2011 at the Olympic Stadium in London. British police will test their ability to respond to attacks and conduct sweeping searches of the venues, locking down security with defensive counter-terrorism tactics developed during the years of Irish Republican unrest. (AP Photo/Stefan Rousseau/PA)

Security forces take part during in a combined British police and British Royal Marines security exercise for the London 2012 Olympic Games on the River Thames in London, Jan. 19, 2012. It is designed to protect the Thames river from possible terrorist attack during the Olympics. (AP Photo/Alastair Grant)

A Rapier air defense system stands with the Canary Wharf business district in the distance during a media event in Blackheath, London, May 3, 2012. Britain's military is carrying out security tests in London ahead of the Olympics , including the deployment of one weapon it hopes it never has to use. (AP Photo/Matt Dunham)

A cameraman films an HVM lightweight multiple launcher in Blackheath, London, May 3, 2012. The British military has insisted that the missiles, with a range of up to 8,000 meters (five miles), could be deployed as the last line of defense. (AP Photo/Matt Dunham)

A Lynx helicopter hovers over a commuter boat during a combined British police and British Royal Marines security exercise on the River Thames, London, Jan. 19, 2012. British police and military forces using a helicopter and inflatable boats teamed up to practice security procedures designed to protect the Thames river from possible terrorist attack during the 2012 London Olympics. (AP Photo/Kirsty Wigglesworth)

Police officers take part in a search exercise at the Olympic Stadium in London, June 19, 2011. British police will test their ability to respond to attacks and conduct sweeping searches of London 2012 venues, locking down security with defensive counter-terrorism tactics developed during the years of Irish Republican unrest. (AP Photo/Stefan Rousseau/PA)

A police woman looks out from a police launch as she takes part in a combined Police and Royal Marines security exercise for the London 2012 Olympic Games on the River Thames in London, Jan. 19, 2012. (AP Photo/Alastair Grant)

Applicants hoping to work as members of security staff at the London Olympics fill out forms as they wait while going through a screening and interview process at a recruitment center near the Olympic Park, Jan. 26, 2012. (AP Photo/Matt Dunham)

Police officers keep watch at Downing Street in Westminster near the London beach volleyball venue, in London, March 28, 2012. Britain's spy agencies and police have planned for a dizzying array of security measures in preparation for the upcoming Olympics. (AP Photo/Kirsty Wigglesworth)

General view of a gated residential flats in Bow, east London, where the Ministry of Defense have warned residents that surface-to-air missiles could be stationed on their rooftops during the London Olympics, April 29, 2012. (AP Photo/Sang Tan)

RAF Typhoon fighter aircraft at RAF base Northolt, where four of the aircraft will be based as part of the Olympics related security exercise in west London, May 2, 2012. (AP Photo/Alastair Grant)

An HVM lightweight surface-to-air missle launcher is displayed during a media event in Blackheath, London, May 3, 2012. The training exercise is designed to test military procedures for the London Olympics. (AP Photo/Matt Dunham)

Royal Navy helicopters carrier HMS Ocean sails through the Thames Barrier on the River Thames in London to dock at Greenwich as part of London 2012 Olympic preparation security exercise, May 4, 2012. (AP Photo/Sang Tan)

Interpol employee looks at finger prints in the control room of the Interpol headquarters in Lyon, central France, June 22, 2012. International police agency Interpol is involved in the security of the London Games. (AP Photo/Francois Mori)