Tanweer's videotape provides more evidence linking the London 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.
Shehzad Tanweer was pictured leaving Pakistan
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.
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.
A video showing London Tube bomber Shehzad Tanweer has been aired on al-Jazeera television.
Tanweer, from Leeds, killed seven people on a train at Aldgate during the attacks on 7 July 2005.
He says on the video: "What you have witnessed now is only the beginning of a string of attacks that will continue and become stronger."
Police said the release of the video on the eve of the bombings' anniversary was designed to cause "maximum hurt".
Tanweer says in a Yorkshire accent on the film that attacks will continue "until you pull your forces out of Afghanistan and Iraq".
It is believed a third man who features in the 31-minute video refers to the Forest Gate raid of 2 June - proving that the video was collated by al-Qaeda in the last five weeks, according to BBC security correspondent Frank Gardner.
The video, the release of which was announced on an Islamist website, includes a statement from Ayman al-Zawahri, al-Qaeda's second in command, and American Adam Gadahn, also known as Azzam al-Amriki.
Gadahn is believed by US authorities to be running al-Qaeda's propaganda operation.
The footage includes people igniting explosives and armed with guns, as well as images of an unidentified man circling points on a map of London.
It is very similar to a video of fellow bomber Mohammad Sidique Khan, released in September 2005.
Both bombers were dressed in a similar way, including headdresses, and the videos had the same "al-Sahab" logo, said to be a signature of al-Qaeda recordings.
The video is likely to add weight to the theory that al-Qaeda was behind the London bombings, Frank Gardner said.
The prime minister's official spokesman said Downing Street would not be giving a reaction to the video.
HAVE YOUR SAY As a practising British Muslim all I can say is that this guy does not represent us Ali Khan, London Send us your comments
He said: "I think we want the attention to focus on the quiet reflection of the nation as a whole and I don't think anything should be allowed to get in the way of that."
Scotland Yard's Assistant Commissioner Andy Hayman said police were aware of the video and that it would form part of their investigation.
"There can be no doubt that the release of the video at this time can only cause maximum hurt and distress to the families and friends of those who died on 7/7 and the hundreds of people who were injured in the terrorist attacks.
"We are sure that the overwhelming majority of all communities are united in condemning any attempt to justify last year's terrorist attacks in London," he went on.
Tanweer killed seven people on a train at Aldgate
A spokesman for the Leeds Muslim Forum, Arshad Chaudhry, said it was very sad that the tape had been released at the time of the anniversary of the bombings, which he called "tragic" for those affected.
"The Muslim community has been very badly affected by [the bombings], particularly in the Beeston and Leeds area," Mr Chaudhry said.
"This will just make life even more difficult, with all the media attention and the rest of the community pointing the finger, which is not justified."
They are still trying to come to terms with what has happened and to see their son on screen will be torture Irshad Hussain, friend of Tanweer family
Tanweer's family were made aware of the video by police on Thursday morning.
They refused to comment on it but a family friend, Irshad Hussain, said the tape's release had been timed to cause maximum damage.
He said: "It shows you what evil people are out there trying to cause anger and frustration.
"It is wrong what he [Tanweer] is saying and everybody knows that, but, unfortunately, there are people who may listen to what he says."
Mr Hussain said Tanweer's parents would be "devastated" to see their son in the video.
"They are still trying to come to terms with what has happened and to see their son on screen will be torture," he said.
London - A year ago, four young British Muslims blew themselves up in a murderous suicide attack on London's transport system. Here is a summary of their background and motives:
Three of the men, Mohammad Sidique Khan, Shehzad Tanweer, and Hasib Hussain all grew up in the Beeston area of Leeds.
Khan, 30, was a teaching assistant at a local primary school working with special-needs children. He was said to have a real talent for working with young people and was highly regarded.
Tanweer, 22, did well at school and went on to study sports science at Leeds Metropolitan University. He was also a gifted sportsman and played cricket for the local team.
Hussain, 18, left school with a few GCSEs at grade C and below. He was quiet at school but was remembered for his large physique and had lost five stone before taking part in the attacks.
Jermaine Lindsay, 19, was born in Jamaica and moved to Huddersfield with his mother. He was said to be successful academically and good at sport. He converted to Islam in 2000 shortly after his mother did. Afterwards his behaviour was said to have changed and he was disciplined at school for handing out leaflets in support of al-Qaeda.
Why did they do it?
There were very few signs of extremism from any of the three Leeds bombers.
In 2001 Khan was said to be serious about religion but spoke out against the 9/11 attacks at his school.
Tanweer was also said to have taken religion seriously from an early age but was said to have been calm and friendly. From mid-2002 he became more focused on religion but no one around him noticed strict religious observance turning to extremism.
Hussain, who once wrote "Al-Qaeda No Limits" on a book at school, was open about his support for the group but did little else to attract attention. He took to wearing traditional Muslim clothing and reading religious texts after undertaking a Hajj visit to Saudi Arabia with his family in early 2002.
Lindsay was believed to have been strongly influenced by an extremist preacher Abdallah al Faisal who was jailed for encouraging his followers to commit murder.
The government has offered little explanation as to the group's motivation.
A video statement by Khan, aired two months after the bombings, said this: "Until we feel secure, you will be our targets. Until you stop the bombing, gassing, imprisonment and torture ... we will not stop this fight. We are at war and I am a soldier."
He also referred to Osama bin Laden and the slain al-Qaeda leader in Iraq, Musab al-Zarqawi as "heroes".
Home secretary John Reid said their motivation was anger at what they perceived to be injustice committed against Muslims around the world and a desire for martyrdom.
Were they directed from abroad?
Khan and Tanweer both visited Pakistan between November 2004 and February 2005. Khan is thought to have received some form of training there.
He is also thought to have had training in a remote part of Pakistan in July 2003, and it is believed he had visited Pakistan and Afghanistan on other occasions from the late 1990s.
The police have concluded there is no evidence to suggest they were directed by al-Qaeda or had any support from the organisation, although the nature of the bombings was typical of attacks carried out by the group.
It is also unclear whether other groups of individuals in the UK were involved in radicalising or helping the bombers in any way. No person has been charged in connection with the attacks.