By Dominic Casciani
Khan: Photographed, not identified
The parliamentary Intelligence and Security Committee has published a detailed review of the intelligence on the 2005 London suicide attacks. The report clears MI5 of failures - and provides immense details into its workings.
What is the purpose of this report?
In 2007, following Britain's then largest terrorism trial, we learned that MI5 had followed two of the London suicide bombers, Mohammad Siddique Khan and Shehzad Tanweer, more than a year before the attacks.
Victims of the 7/7 bombings and bereaved families pushed for a public inquiry - but instead the prime minister asked the Intelligence and Security Committee (ISC) too look again at the evidence.
So what did the committee find?
In brief, the ISC concludes that MI5 did nothing wrong - because it was not in a position to know what Khan and Tanweer would go on to do.
As a crude measure, to provide comprehensive intelligence coverage would require several hundred thousand officers as opposed to their current 3,500. This would be unachievable and unacceptable
The reason why it did not know is because of the unprecedented events of 2004.
MI5 was struggling to cope with a huge number of terror leads. During February and March its officers were investigating men involved in a massive plot to detonate a homemade fertiliser bomb.
Omar Khyam was the ringleader of that plot, and the investigation was codenamed Operation Crevice.
Khyam knew Mohammad Siddique Khan. Khan was seen meeting Khyam four times in the UK. Bugs revealed that Khan was asking about fraud and advice about going overseas.
Officers classed the then unidentified man as "desirable" rather than essential. They followed him to Leeds - but concluded they had more urgent priorities.
What pressure does MI5 say it was under?
We do not know how many people MI5 is capable of watching in one go.
SURVEILLANCE MI5 GAVE TO TARGETS IN 2004
Good coverage: 0.13%
Less good (some gaps): 6%
Significant gaps: 33%
No coverage: 19%
But we know how many people it was not watching in 2004.
The ISC says that 52 targets whom MI5 classed as essential - people likely to be involved in or know about terrorism - were not being followed.
Within months of Crevice being cleared up, officers mounted an enormous operation against a cell later convicted of equally serious plotting.
Exactly what did the police and MI5 then know about Khan?
It's now emerged that Siddique Khan was among 40 men observed by West Yorkshire Police attending a training camp organised by "two known extremists" in 2001. Khan's image was among 31 of the men who police could not identify. They had a picture, but no name.
Two years later, a police team following an extremist saw him given a lift in a car registered to a Siddique Khan. It was a brief contact, says the report.
How did MI5 come across the later bombers?
The ISC says the earliest MI5 knew of Siddique Khan was on 13 July 2003 when they were following a Luton man called Mohammed Qayum Khan. One of the numbers he rang was registered to a "Siddique Khan".
The address connected to the number was the bookshop we now know to have been used by Khan to distribute extremist literature. During the 7/7 investigation, three other calls in 2003 by the Luton man were linked to Khan. MI5 says there was nothing to suggest at the time that these calls were significant.
West Yorkshire Police was later given some information to look into - but their checks yielded nothing suspicious, says the report.
Did MI5 completely discount Khan at this stage?
The ISC says: "When MI5 knew that Khyam was an attack planner he was seen to meet UDMs [unidentified males who were later established to be Khan and Tanweer]. There was no intelligence to show whether the UDMs were suspicious or innocent until the final meeting when they were heard discussing financial fraud. This was sufficient for MI5 to run routine checks and exchange information on them with [police]. However given that they were not discussing attack planning and did not pose a threat to life, they were not made priority targets."
What does this amount to?
Before 7/7, Khan's name had appeared on a number of occasions in different places and apparently unconnected incidents. There were pictures of an unidentified man, who we now know to be Khan, with a target. But MI5 insists there was no intelligence of a threat. There were lots of dots - but dots that were not joined up.
Why were they not joined up?
It was fragmentary evidence. In theory, had the resources been there, MI5 could have connected all the information - but it says that it would not have made a difference because there was still nothing to suggest he was a danger.
The ISC report provides an interesting insight on this point. It says that MI5 starts any investigation by trying to work out what someone is up to - and only then seek to establish who they actually are.
Jonathan Evans, the director general of MI5, told the ISC during evidence that were officers asked to go through every single scrap of information in detail, they would only get 20% of their current workload done, rather than allowing them to focus on immediate threats.
Does the report say anything about claims of a "fifth bomber?"
This allegation stems from the large amount of explosives that was left behind in the Leeds bomb factory and the presence of small devices in the car the men used to reach Luton, before joining trains to London.
MI5 now think that someone else might have been involved in the plans - but the intelligence is so "fragmentary" that it cannot be verified and there is nothing that can remotely be classed as evidence. Both MI5 and MI6 assess that there was some direction from al-Qaeda overseas.
Does this report moves us any closer to the truth?
The ISC believes its report is the last word. It's even devoted a page to debunking one of the infamous conspiracy theories around the bombings.
But it looks like the report doesn't satisfy many of the 7/7 survivors and families. Many of them are considering legal action to force the government to hold a public inquiry.
They argue that the report does not see the wood for the trees; they argue the report fails to ask legitimate questions about MI5's approach to investigating a serious terrorist network. They say the evidence was there to see that in 2004 Khan was on the ladder of extremism - just a few rungs short of the top.