Q&A: 7 July 2005 attacks inquests
The inquests into the deaths of 52 people killed in the 7/7 bombings will last many months. BBC News explains what will happen at the hearings.
What is the coroner's role?
Suspicious, accidental and violent deaths are investigated at inquests so that society can learn from what has happened.
It has taken more than five years for the inquests into the 7 July attacks to come to full hearings because they were adjourned while the police investigated the bombers.
Lady Justice Hallett, a Court of Appeal judge, was appointed to be coroner into the deaths. Despite the time that had passed, she said that the inquests should be resumed because important questions needed answering.
Aren't all the facts already known?
There is a great difference between knowing the basic details of what happened and knowing enough to be able to understand exactly how the attacks took place and why people died.
For example, we know the locations of each attack - underground trains just Aldgate, Edgware Road and Russell Square Tube stations, and on a double-decker bus in Tavistock Square, near King's Cross - and who died at each location.
But some of the families only learnt recently that their relatives did not die instantly. The fact that 17 initially survived therefore raises questions about whether anything could have been done to save them. This is the kind of question an inquest sets out to answer.
So what else will the inquests cover?
Lady Justice Hallett has a list of key issues that includes establishing the movements of the bombers and the precise circumstances at each attack location.
The inquest is looking at the emergency services' response, plans for dealing with terrorist incidents of this kind and, critically, whether the bombers could have been stopped.
That means Lady Justice Hallett will be looking at what MI5 and the police knew about the bombers, when they knew it and whether it amounted to anything significant.
Who will be called as witnesses?
The key evidence is coming from anyone with first-hand knowledge of the attacks - those who witnessed and survived them and those who rushed to the scene.
The inquest will then broaden by taking evidence from the emergency services involved in planning the response to such events. The final and most difficult stage of the inquests will concern the question of "preventability".
So what did MI5 and the police know?
MI5 came across two of the bombers, Mohammad Sidique Khan and Shehzad Tanweer, on the periphery of another investigation in 2004.
Surveillance officers saw the pair meeting an extremist involved in this separate bomb plot.
Other fragments of evidence about Khan's activities have since emerged - but the question is whether these fragments would have been enough to make Khan an "essential target" for security service surveillance.
In in a document published by MI5 in 2007, the agency argued that it could only piece together the information, including Khan's name, after the attacks.
Parliament's Intelligence and Security Committee, which reviews MI5's operations, concluded in a report that the service had not failed.
But some victims' families and survivors denounced the ISC's findings as a whitewash.
The former Labour government ruled out a judicial or public inquiry and the families inevitably looked to the inquests as their next best hope of asking tough questions.
Can the inquest answer their questions?
Lawyers for the security service warned during the pre-inquest hearings that investigating the service would encourage terrorists.
They said it was metaphorically akin to handing over the keys to Thames House, MI5's headquarters.
Lady Hallett said she recognised that there might be national security limits on what could be examined as part of the inquest and members of her inquest team have already visited the security service's London headquarters to discuss some of the secret documents.
Can the coroner hold secret hearings on national security grounds?
Counsel for the government argued that Lady Hallett could - but in November she ruled that she would not exclude families from the hearings.
She has now told the Security Service to take necessary steps to remove names, sources or other sensitive information from documents that can then be used to tell the story, without compromising legitimate secrecy.
So what's going to happen?
It's not currently clear how the inquests will progress if there is a situation where Lady Justice Hallett and her team want to introduce MI5 material which the police, security service or government believes should remain secret - and the higher courts rules against her.
The coroner has warned the government that she cannot halt the main inquests just to launch a parallel but semi-secret inquiry into MI5's role.
"There remains the very real possibility that these inquests would have to be adjourned and the whole process restarted," she said in her judgement on the question.
What about survivors? Will they feature in the inquest?
About 700 people were injured in the attacks, some of them severely.
Lady Hallett ruled that the survivors did not meet the legal criteria to be named as "interested parties", but that she expected that a great number of survivors would give important testimony of what they saw and heard.
What about the inquests for the bombers?
They are currently adjourned. None of the bombers' families appeared or were represented at the pre-inquest hearing. The solicitor for some of the bombers' families had initially planned to attend but did not do so after being denied legal aid funding.
Why have the inquests taken five years to happen?
Many inquests are held within months because the circumstances are fairly simple to establish. But the amount of work required to establish what happened on 7 July 2005 has been vast.
Police investigated thousands of phones and phone calls, collected 13,000 exhibits - and forensically examined 7,000 of them. More than 18,000 statements were taken.
The investigation led the police to three friends of the bombers - and in 2007 they were charged with helping the attackers. Two years later, the trio were acquitted of that charge - and the criminal investigation came to a halt.
Once the police and prosecutors concluded they would not be charging anyone else, the Coroner received the green light to resume the inquests.