LONDON (AP) — British lawmakers said Tuesday that two al-Qaida-inspired extremists who murdered a British soldier in a London street had been under scrutiny by the intelligence services, and one had expressed his intention of killing a soldier in an online exchange months before the attack.

Parliament’s Intelligence and Security Committee said that if British spies had known of Michael Adebowale’s declaration, “there is a significant possibility” they could have prevented the May 2013 murder.

But the online exchange was only discovered after Adebowale and Michael Adebolajo killed Fusilier Lee Rigby.

The lawmakers concluded that spy agencies had made mistakes, but that with the knowledge they had at the time they “were not in a position to prevent the murder.”

In a report on what the intelligence services knew about the killers, the committee said the two men had shown up on spy agencies’ radar in seven different investigations and that in two of them Adelobajo had been labelled a “high priority.”

Adebolajo was arrested in Kenya in 2010; authorities said he was trying to travel to Somalia to join the militant group al-Shabab.

The committee was critical of Britain’s foreign intelligence agency, MI6, for waiting four months before opening an investigation into Adebolajo after he returned.

The report was highly critical of U.S.-based communications companies such as Google, Twitter and Yahoo for failing to report extremist content or comply with requests from British agencies to hand over information.

It said that the companies “should accept they have a responsibility to notify the relevant authorities when an automatic trigger indicating terrorism is activated and allow the authorities, whether U.S. or UK, to take the next step.” It said the companies should avoid using customers’ privacy as a reason for not doing so.

Adebolajo and Adebowale are serving life sentences for murdering 25-year-old Rigby, who was run down with a car before being attacked with knives.