The killing of British soldier Lee Rigby by extremists on home soil could have been prevented if a US internet company had flagged up online messages to UK intelligence, a government report has said.
The unnamed company unintentionally provided "a safe haven for terrorists" by failing to alert MI5 of an exchange between killer Michael Adebowale and an extremist overseas, the UK parliament's intelligence and security committee claimed in the report published on Tuesday.
The committee was also highly critical of the company's refusal to fully cooperate with the UK government surveillance agency GCHQ and called for all communication service providers to review terrorism "trigger" accounts and notify authorities.
It said that British citizens are "unnecessarily exposed to greater risk" because of the "considerable" difficulty UK intelligence agencies have in accessing online communications from US providers such as Apple, Facebook, Google, Twitter, BlackBerry, Yahoo and Microsoft.
Rigby, a 25-year-old soldier who had served in Afghanistan, was killed near Woolwich Barracks in south London on 22 May 2013. He was off duty when Adebowale and Michael Adebolajo ran him down with a car and attacked him with knives and a cleaver, almost hacking off his head. His mutilated body was dragged into the road before the men charged at armed police who shot and wounded them. Rigby, a separated father with a two-year-old son, was engaged to a new fiancee at the time of his death.
The pair had appeared in seven different intelligence agency investigations, but staff did not have enough intelligence to prevent Rigby's murder, the committee said.
However, an online exchange in December 2012 between Adebowale and an extremist overseas, which did not come to light until after the attack, "could have been decisive," the report said.
In the exchange Adebowale expressed his desire to murder a soldier "in the most graphic and emotive manner" because of UK military action in Iraq and Afghanistan.
The report said the individual Adebowale was communicating with suggested several potential attack methods, ranging from martyrdom — a suicide bombing — to a knife.
Adebolajo — who was once arrested by authorities in Kenya on suspicion of trying to train with al-Shabaab militants — was a high priority for MI5 and under surveillance using "a broad range of intrusive techniques." However Adebowale was a low-level subject of interest.
The US company had automatically suspended four of Adebowale's 11 accounts before the murder because they set off terrorism "triggers," the report said.
GCHQ told the committee that the company had not flagged up the online exchange before the killing and, following the murder, had refused to provide them with detailed explanation of the reasons behind all of the account closures.
The report added that at any one time MI5 is running several hundred investigations and monitoring "several thousand individuals" linked to Islamic extremist activities in the UK.
Responding to the report, British Prime Minister David Cameron told the parliament: "A number of companies have improved their cooperation, but […] there is much further to go.
He added: "Terrorists are using the internet to communicate with each other and we must not accept that these communications are beyond the reach of authority or of the companies themselves.
"Their networks are being used to plot murder and mayhem. It is their social responsibility to act on this and we expect them to live up to this responsibility."
However, Amandla Thomas-Johnson, a spokesperson for CAGE, which campaigns on behalf of communities disproportionately affected by the war on terror, criticised the inquiry for shifting the blame from intelligence agencies to communication service providers.
He told VICE News: "The Woolwich inquiry targets internet service providers and freedom of speech.
"This is a clear excuse to grant security agencies even more power over British society, when these powers haven't been working to combat extremism for the last 13 years."
Follow Ben Bryant on Twitter: @benbryant