LONDON, ENGLAND - MAY 24:  A police officer stops to look at flowers laid close to the scene where Drummer Lee Rigby of the 2nd Battalion the Royal Regiment of Fusiliers was killed, on May 24, 2013 in London, England. Drummer Lee Rigby of the 2nd Battalion the Royal Regiment of Fusiliers was murdered by suspected Islamists near London's Woolwich Army Barracks. The UK's security services are facing a Commons inquiry after confirmation that the two men arrested were known to MI5.  (Photo by Dan Kitwood/Getty Images)