MI5 faces inquiry into intelligence on suspects One of the Woolwich terror suspects Britain's security services were last night facing questions over what they knew about the suspected killers of a British soldier in Woolwich as Scotland Yard made further arrests in what they called a "large, complex and fast-moving" investigation. Both main suspects were known to MI5, the domestic security service, before the incident, prompting a parliamentary inquiry into how the agency handled intelligence material relating to the two men. As the alleged killers remained under armed guard in hospital, police were racing to establish whether others were involved in planning the attack. Counter-terrorism officers made two arrests on suspicion of conspiracy to murder and searched five properties in London and one in Lincolnshire. On a day that saw the identities of one of the killers and of the victim revealed, Whitehall officials let it be known that the suspected attackers were both on MI5 files before this week's brutal murder. The officials said MI5 had not come to the view before this week's killing that either of the men was likely to carry out a violent extremist attack in the UK. However, the revelation is certain to raise questions about operations at the security service, whose funding has been significantly boosted since the 2005 London bombings that killed 52 people. MI5 was heavily criticised after the 2005 bombings because some of the perpetrators had initially been under surveillance but were later dropped from investigation because they were not deemed a threat. Sir Malcolm Rifkind, the former Conservative foreign secretary who chairs parliament's Intelligence and Security Committee, said he had been fully briefed on the attack by Andrew Parker, the new director-general of MI5. "There are quite legitimate questions at this stage as to whether the intelligence agencies were in touch with these guys and if not, why not?," Sir Malcolm told the Financial Times. Security experts argue that MI5 and the police have records on many Islamist extremists in the UK. In 2007, Jonathan Evans, former head of MI5, said there were at least 2,000 people in the UK who "pose a direct threat to national security and public safety." However, security experts say MI5 has to constantly assess which of these might go on to plot acts of violence and therefore need to be pursued with greater intensity. "Everything we have seen about this attack - such as the basic nature of the weapons and the fact the gun didn't work - suggest this was a crude operation and one that was hastily drawn up," said Michael Clarke of the Royal United Services Institute, a think tank. That means it would have been very difficult for the agencies to predict that these people were going to carry out an attack like this. Jamie Bartlett of Demos, another think-tank, said: "The intelligence agencies have disrupted a lot of the co-ordinated and highly skilled jihadist networks. Those interested in violence these days are amateurish and almost more interested in the violence of the deed than any underlying ideology. They are therefore far more difficult to spot The Ministry of Defence announced that the victim of Wednesday's attack was Drummer Lee Rigby of 2nd Battalion, The Royal Regiment of Fusiliers. He was 25 and had a two-year-old son. One of the suspected killers was Michael Adebolajo, a Briton of Nigerian descent. Reports indicated he comes from a devout Christian family but took up Islam after leaving college in 2001. Mr Adebolajo was known to the authorities for handing out radical Islamist pamphlets in Woolwich. Anjem Choudary, an Islamist cleric, told Reuters that Mr Adebolajo was known to fellow Muslims as Mujahid - a name meaning "warrior." Mr Choudary said Mr Adebolajo had converted to Islam in 2003 and had attended meetings of the banned Islamist organisation al-Muhajiroun. The other suspected killer - who as of last night was unnamed - was widely reported to have been born in Nigeria and to be a naturalised UK citizen. US President Barack Obama said: "I condemn in the strongest terms the appalling attack against a British service member in Woolwich on May 22. The United States stands resolute with the United Kingdom, our ally and friend, against violent extremism and terror.