A parliamentary watchdog has blamed Facebook for failing to prevent the murder of Fusilier Lee Rigby, it was claimed today.
While the Intelligence and Security Committee (ISC) report doesn't mention the social network, both the BBC and The Telegraph claim to have learned that it was Facebook that could have flagged a "graphic and emotive" discussion between Michael Adebowale, one of Rigby's killers and an overseas extremist.
The report said there was a "significant possibility" that the information could have led MI5 and MI6 to stopping the attack before it occurred.
It's claimed that without Facebook's help the security services remained in the dark, the report said. While MI5 and MI6 are accused of making mistakes, it is the net firms that are targeted most directly for failing to stop the attack near Woolwich barracks on May 22 last year.
The report concludes that the social network has made itself a "safe haven for terrorists" because messages sent within its service were inaccessible to GCHQ, MI5 and MI6.
The full report called, in a wider sense, on firms including Facebook, Apple, Google, Microsoft, Twitter and Yahoo to do more to prevent terrorist attacks, and to work more closely with security forces, despite their privacy commitments to users.
Prime Minister David Cameron agreed with the report's conclusions, telling the Commons:
"The committee is clear and I agree that they have serious concerns about the approach of a number of communication service providers based overseas."
"Terrorists are using the internet to communicate with each other and we must not accept that these communications are beyond the reach of the authorities or the internet companies themselves."
"We will continue to do everything we can. But crucially we expect the internet companies to do all they can too.
"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 that responsibility."
Adebowale was in contact with an extremist now know to have links al Qaida in the Arabian Peninsula in late 2012, the report said. But this was not revealed until an unidentified third party notified GCHQ after the attack.
In the exchange, he expressed his desire to murder a soldier in retaliation for UK military action in Iraq and Afghanistan, although he had not developed a plan as to how he might carry out an attack - but the extremist advises him on different methods including using a knife.
It later emerged that a number of online accounts owned by Adebowale were automatically disabled due to association with terrorists and terrorism - but the web firm was unaware as it does not manually review such decisions.
Nor did the firm, which the ISC refuses to name, notify law enforcement agencies.
But Jim Killock, executive director of Internet rights organisation Open Right Group said the government was using the murder to justify further impositions on privacy:
"The government should not use the appalling murder of Fusilier Rigby as an excuse to justify the further surveillance and monitoring of the entire UK population. To pass the blame to internet companies is to use Fusilier Rigby's murder to make cheap political points.
"The committee is particularly misleading when it implies that US companies do not co-operate, and it is quite extraordinary to demand that companies pro-actively monitor email content for suspicious material. Internet companies cannot and must not become an arm of the surveillance state.
"As the report admits, 'lone wolf attacks' are almost impossible to predict - and therefore difficult to prevent. The security services should focus their efforts on the targeted surveillance of individuals like Michael Adebolajo rather than continuing to monitor every citizen in the UK."
Addressing a press conference at Parliament, Conservative MP Sir Malcolm Rifkind said: "The one issue which we have learned of which, in our view, could have been decisive only came to light after the attack.
"This was an online exchange in December 2012 between Adebowale and an extremist overseas, in which Adebowale expressed his intent to murder a soldier in the most graphic and emotive manner.
"This was highly significant. Had MI5 had access to this exchange at the time, Adebowale would have become a top priority. There is, then, a significant possibility that MI5 would have been able to prevent the attack."
Sir Malcom said the US firm "could have made a difference".
"However, this company does not regard themselves as under any obligation to ensure that they identify such threats, or to report them to the authorities," he said. "We find this unacceptable - however unintentionally, they are providing a safe haven for terrorists."
Muslim converts Adebolajo and Adebowale ran down Fusilier Rigby, who was dressed in a Help For Heroes hoodie, in a Vauxhall Tigra near Woolwich Barracks, in south east London, before savagely attacking the defenceless soldier as he lay in the road.
The ISC inspected hundreds of highly-classified documents and questioned ministers, the heads of the three agencies and senior officers from the Metropolitan Police for its inquiry - described as the most detailed report the group of MPs has ever published.
The fanatics appeared, between them, in seven different agency investigations, the ISC said, which contained "a number of errors" including processes not being followed, decisions not being recorded, or delays.
But the group of MPs added: "We do not consider that any of these errors, taken individually, were significant enough to have made a difference.
"We have also considered whether, taken together, these errors may have affected the outcome.
"We have concluded that, given what the agencies knew at the time, they were not in a position to prevent the murder of Fusilier Rigby."
Human rights group Liberty said the ISC had "shamelessly" spun the facts in a bid to shift the blame on to communications companies and away from the intelligence agencies.
Isabella Sankey, director of policy for Liberty, said: "The ISC shamefully spins the facts seeking to blame the communications companies for not doing the agencies' work for them."