By Dominic Casciani
The police watchdog report into the death of Jean Charles de Menezes has shone a light onto controversial "shoot-to-kill" tactics for dealing with suicide bombers - but what role did they play on the day he was killed?
Shooters: Officers C2 and C12 looking for their suspect
When the men responsible for the 2004 Madrid train bombings blew themselves up as police closed in, taking with them an entire apartment block, it was the clearest possible signal that tactics to apprehend major terrorism suspects needed to be radically different from those employed during normal policing procedures.
Faced with such a threat, how are police officers supposed to act to protect themselves and the public?
That is the issue at the heart of Operation Kratos, the suicide bomber tactics, that the Independent Police Complaints Commission wants us to debate two years on from the death of Jean Charles de Menezes.
The Brazilian electrician died when two specialist firearms officers shot him seven times as he sat on a London Tube train on 22 July 2005.
They thought he was a suicide bomber who had to be stopped at all costs. But the Kratos strategy had not been activated that morning - no codeword had been given for them to fire on its terms.
Kratos is commonly thought of as a shoot-to-kill policy. The reality is that Kratos is less a policy and more a series of critical linked tactics that operationally underline the severity of the operation.
Kratos includes three key elements:
A "directed shot" - an order to shoot from an operations commander
A critical shot to the head to instantly incapacitate, almost inevitably killing
A lack of warning because a suicide bomber may detonate
Kratos tactics must be sanctioned by a "Designated Senior Officer" (DSO) - a senior commander with specialist training. Deputy Assistant Commissioner Cressida Dick was the DSO on the day that Mr de Menezes died - but at no point did she give the Kratos codeword.
Where the confusion arises, say investigators, is that each element of Kratos already appears in the main firearms policies.
Take a directed shot, for instance. Armed teams are often at the end of a long chain and may know very little about the people they are confronting.
This means that commanders across all the detail of an operation must have the authority to order an officer to shoot if they believe it is necessary.
Then there is a second separate strategy for dealing with a suspected suicide bomber targeting a major public event, such as the Trooping of the Colour.
In this case, a commander has the authority to order a sniper to fire without warning from a hidden position.
The debating point, say investigators, is whether bringing key elements together under the Kratos umbrella, and the psychological and operational impact that has in a fast-moving crisis, makes it more likely that someone was going to get shot. Some critics fear the very existence of Kratos in its current format creates an air of inevitability.
During the trial of the Met Police for breaching health and safety laws, the jury heard that on 22 July 2005 firearms teams were psychologically pumped up for a life-or-death confrontation with a suicide bomber.
The officers took 124-grain ammunition - a form of "dum dum" bullet designed to kill more swiftly - critical to stopping a bomber in his tracks.
But at the same time, officers had different views of their operational parameters.
Mr de Menezes was followed to Stockwell station and shot dead
The two officers who shot Mr de Menezes, codenamed C2 and C12, had taken authority to make a "hard stop" of the suspect - but at the same time they did not believe Kratos had been sanctioned.
But another detective superintendent in Scotland Yard's Room 1600 operational control told the IPPC that he had heard Cmdr Dick say the "male must not be allowed to get on a train at all costs".
Firearms officers C11 and C6 interpreted this as an instruction from the DSO. Another, C6, told the IPCC he had believed he might have had to shoot the target to stop him killing members of the public and himself.
William, an armed officer close to the killing but not involved, believed he had been involved in a Kratos incident.
Vic, another armed officer, explained how he had interpreted orders from Trojan 84, a key superior.
"The tone of voice and urgency of this radio transmission, combined with the intelligence meant to me that he must be stopped immediately and at any cost. I believed that a bombing of the Tube could be imminent and must be prevented."
What this comes down to, say investigators, is the need to embed Kratos in a broader approach to firearms - and for more clarity in command structures, orders and language.
Deborah Glass, an IPCC commissioner, has studied firearms tactics and says the public need to have a better understanding of the reality of armed operations.
"The difficulty with having an operation called Kratos that is specifically about suicide bombers is that there is an implicit assumption that you are going to be always dealing with suicide bombers," she says. "You are giving it a level of certainty that does not appear in real life.
"So the problem can well be that if you create a mindset in firearms officers that you are dealing with a suicide bomber then the concerns commanders would have about what is the level of the threat may well be overtaken."
In the past year the Met responded to 10,000 potential firearms incidents and officers fired only three times.
Each of those deployments relied on highly trained officers being able to make split-second judgements on the nature of the threat they faced.
The concerns about Kratos and broader firearms strategies are not necessarily about those split-second judgements - they are about the command and control that surrounds them - and the effect it has on the decision to pull the trigger.