By Gordon Corera
BBC security correspondent
The video of London bomber Shehzad Tanweer shown on al-Jazeera TV on the eve of the attack's first anniversary provides more evidence linking the bombers to al-Qaeda.
But questions still remain, and the answers to many of those questions lie in Pakistan.
In the wake of last July's bombings, it did not take long for Pakistan to become almost as much a focus of attention as the Yorkshire base of the bombers.
Were the men really home-grown terrorists or were they directed by al-Qaeda? What was the significance of their time in the country where much of the remaining al-Qaeda leadership is thought to operate?
Officials have been cautious in confirming that a direct link exists between the men and those around Osama Bin Laden.
"It is not easy to find out what happened... such information as we do have does suggest there is probably a link to al-Qaeda," Peter Clarke, head of anti-terrorism at the Metropolitan Police, told the BBC earlier in the week.
What evidence is there linking the bombers to al-Qaeda in Pakistan?
We know, from official reports, that two of the bombers - Shehzad Tanweer and Mohammad Sidique Khan travelled together to Pakistan between November 2004 and February 2005.
No one knows for sure what they did out there but the suspicion will be that this is when both men made their videotaped testimonies.
Khan also travelled to Pakistan on at least one earlier occasion and may have been to Afghanistan in the late 1990s or soon after.
British intelligence agencies believe some form of operational training is likely to have taken place while Khan and Tanweer were in Pakistan together and that it is likely they did have contact with al-Qaeda figures.
Pakistani intelligence sources have suggested the men may have met with al-Qaeda's number two, Ayman al-Zawahiri, in Pakistan's tribal areas sometime in January 2005. British officials say they have no evidence confirming the meeting but they don't discount the possibility that it took place.
Shehzad Tanweer was pictured leaving Pakistan
Whoever the bombers met, straight after their return, Khan and Tanweer began putting in place the key elements of their plan. They both left their jobs, rented a place in which to build the bombs and began purchasing material.
And in the three months leading up to the bombing, the men were in contact with an individual or individuals in Pakistan who may have been giving them advice and direction.
It is not known who it was or the exact nature of the contacts but the methods used, designed to make it difficult to identify the individual, makes the contacts look suspicious.
When I met some of Pakistan's top counter-terrorist officials during a visit earlier in the year, they declined to speak on the record.
The notion that it was Pakistan rather than the UK that was responsible for the bombers' radicalisation raises particular ire
But they did say they had been given 299 telephone numbers in Pakistan linked directly or indirectly to the bombing - but had not found a mastermind.
They argued that al-Qaeda's leadership did not have the capability to plan or direct operations because it was under pressure.
But in recent months Western intelligence agencies have begun shifting away from the notion that al-Qaeda has largely become an ideology rather than a structured operation, to once again believing that there remains some capability for direct operational planning within al-Qaeda's leadership.
There are sensitivities in Pakistan over any links to 7 July. Pakistani officials strongly reject the notion that they are not co-operating fully in fighting terrorism and point to the deaths of soldiers fighting in the wild border region of Waziristan.
And the notion that it was Pakistan rather than the UK that was responsible for the bombers' radicalisation raises particular ire.
"If an individual commits an act who was bred and brought up and educated not in Pakistan but elsewhere and since he visited Pakistan for a few days or weeks (it) does not mean that it is Pakistan that is responsible in his conversion as (a) terrorist," Major General Shaukat Sultan, Pakistan's military spokesman explained.
Another problem is the growing complexity of al-Qaeda.
"There is very much an integration between the Pakistani jihadi community and al-Qaeda's leadership and I think this is the galaxy that spawned the 7 July bombings," explains Alexis Debat, a counter-terrorism expert.
"But it's very hard for investigators to find out where the Pakistani jihadi community stops and al-Qaeda starts. And it's much more difficult for the Pakistani government to go after the Pakistani jihadis."
The coincidence of al-Qaeda basing itself in Pakistan, increasingly overlapping itself with Pakistani jihadist groups and the high transit of people from Britain's Pakistani community back to the country makes investigating links and travel particularly difficult.
There were 400,000 visits by UK residents to Pakistan in 2004 - and the average length was 41 days.
There is considerable intelligence liaison between Pakistan and countries such as the US and UK. But it is always on Pakistan's terms.
Shehzad Tanweer warned of further attacks
According to Pakistani officials, when someone is picked up, Pakistani interrogators will talk to them first and begin by asking them about any threat within Pakistan.
If they later divulge any information about threats to another country, officials from that country are told and may be invited to become "actively involved" in the investigation.
This may involve watching an interrogation take place through video monitors.
If the Pakistani officials decide to allow direct interrogations to take place by a foreign intelligence service then this will be done jointly, with Pakistani officials present.
This might involve officers from the CIA or FBI in the US or MI6 or MI5 in the UK (MI5 is the domestic security service but tends to push to take the lead in foreign investigations where there is a possible threat to UK security).
A year on, the exact role of the bombers' travels to Pakistan in the run-up to the attack remains unclear but the evidence pointing to a major role for al-Qaeda is mounting.