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A report into the 2013 Islamist murder of British soldier Lee Rigby has concluded that his death might have been avoided if an unspecified web firm — subsequently identified by the BBC as Facebook — had notified domestic security agency MI5 of an exchange between the killer, Michael Adebowale, and another extremist.

The report, issued by the U.K. Parliament’s Intelligence and Security Committee (ISC) on Tuesday, cleared MI5 of major failings but claimed that the exchange would have been “the single issue which – had it been known at the time – might have enabled MI5 to prevent the attack” by stepping up surveillance on Adebowale. The killer had repeatedly been under surveillance, but was not seen as a high-level threat.

The report said the “internet company” had previously closed some of Adebowale’s accounts because its automated system had flagged up terrorist associations, but did not pass on this information to the authorities. The subsequent exchange in question, which the company’s systems did not flag at the time, graphically described Adebowale’s intent to murder a soldier.

The report stated:

We take the view that, when possible links to terrorism trigger accounts to be closed, the company concerned – and other Communications Service Providers – should accept their responsibility to review these accounts immediately and, if such reviews provide evidence of specific intention to commit a terrorist act, they should pass this information to the appropriate authority. On the basis of the evidence we have received, the company does not have procedures to prevent terrorists from planning attacks using its networks… We further note that [web firms] attributed the lack of monitoring to the need to protect their users’ privacy. However, where there is a possibility that a terrorist atrocity is being planned, that argument should not be allowed to prevail.

There is, of course, always a possibility that any platform or space is being used to plot a terrorist act, be it a social network or a bar. By this logic, there should never be privacy, and everyone that facilitates communication between people should police what they say.

Echoing the recent words of new GCHQ spy chief Robert Hannigan, the report went on to say that the difficulty British spies face in accessing data from U.S. web service providers was “of great concern.” Edward Snowden’s revelations about NSA-GCHQ cooperation and programs such as PRISM would indicate otherwise.

British ISPs recently agreed to filter out extremist material from what people in the country can see online. I have little doubt that the Rigby murder will be used as justification for further censorship and surveillance in the U.K., by those who believe that communications service providers should act as police for what their customers do with their services.

UPDATE (5.30am PT): That didn’t take long. In Parliament, Prime Minister David Cameron just said that “things need to change” regarding “the role and responsibilities of internet companies in helping to keep us safe.” He added that new legislation was needed to make sure the government could intercept all internet communications.

This article was updated at 8.40am to note that the internet company was, according to the BBC, Facebook.