By Crispin Black
Intelligence analyst, Janusian Security Risk Management
There is speculation the attacks in London were by suicide bombers
Police in London now believe last Thursday's bombings were carried out by four men who all probably died.
Former government intelligence analyst Crispin Black gives his views on the difficulties of fighting extremists prepared to die for their cause.
Suicide bombers carry both an explosive and a psychological/propaganda charge.
Their main advantage as a weapon is penetration - traditional security measures which usually rely on the idea that the terrorist wants neither to be caught nor to be killed are easily bypassed.
Nor does the terrorist have to expend time and effort on an escape plan - often the most demanding and risky part of an operation. They are also accurate - the bomb can be delivered precisely to where it is needed - useful for assassinations.
The Tamil Tigers managed to kill both a former Indian prime minister, Rajiv Gandhi, and a president of Sri Lanka, Ranasinghe Premadasa, using female and male suicide bombers respectively.
Indeed the Tamil tigers are statistically the most successful and ruthless practitioners of suicide bombing - a useful corrective to those who regard it as an Islamist extremist phenomenon.
The psychological and propaganda effects are often more shocking and insidious than the physical destruction.
Suicide attacks can hardly be classified as "cowardly" - the usual (and re-assuring) term of contempt for terrorists who are prepared to kill remotely while minimising the risk to their own lives.
There is always the uncomfortable suspicion that if individuals are prepared to die for a cause, that cause must have some validity - this notion has been exploited to great effect by the Palestinians.
But probably the worst characteristic of suicide bombers, in the context of Islamist extremists in the West, is that they are likely to be particularly effective at setting communities against each other.
Police are searching houses linked to three suspects
It is one thing to be suspicious that a passenger travelling with you on public transport might be trying to plant a bomb - you can raise the alarm or call the police - quite another to suspect that a fellow passenger might actually be a bomb about to go off.
The fear and dread are multiplied many times over and suspicions will inevitably focus on what people look like.
Suspicions are likely to be re-inforced by the fact that it is not possible generally for suicide bombers to emerge within communities unless somewhere within that community there is a source of either theological or social validation.
In this sense those that preach suicide martyrdom are every bit as responsible as those who actually do it.
But suicide bombers do have vulnerabilities. They are usually supported by a command and supply chain. The bomber has to be briefed, fed and watered, accommodated in a safe house and delivered to the target by a support team.
Typically, that support team will have selected the targets and carried out detailed reconnaissance of both the target itself and any other relevant factors - routes and security measures such as CCTV coverage.
The final confirmatory recce and rehearsal is usually carried out by the bombers themselves, shortly before the operation but accompanied by members of the support group.
Maintaining the exalted religious state of the bombers is likely to be the most difficult pre-operational task and it usually requires the presence of a groomer or mentor.
Suicide bombers can go off the boil after a while with all the attendant security risks - you have to work hard at keeping them at the correct pitch.
Crucially, few if any members of the support team have any interest in martyrdom themselves. They can be deterred by traditional security measures - they are the weak point that over time the forces of law and order can exploit.