By Dominic Casciani
BBC News home affairs
Slow work: Scientists could take months to examine car bomb
The first car bomb found in central London on Friday morning has been taken to a specialist maximum security laboratory.
The Forensic Explosives Laboratory has experts on around-the-clock stand-by to deal with terrorist incidents.
Once a device such as a car bomb is made safe, it is taken to the small team based in a complex hidden away in the Kent countryside.
The scientists painstakingly examine car bombs in the specialist "X47" laboratory built during the IRA era.
The X47 building complex most recently housed the remains of the bus blown apart by one of the 7 July 2005 London suicide bombers.
The Forensic Explosives Laboratory and its 60 staff deal with the remains of bombs - or unexploded bombs used against the UK or British interests, such as UK forces abroad.
While the 130-year-old laboratory is an arm of the Ministry of Defence, much of its work is with police forces, dealing with all types of incidents from reckless garden-shed experimenters through to the attacks on 7 July 2005.
The small team of scientists are hand-picked through a specialist recruitment programme. It takes up to four years to build up the expertise needed to become a qualified case officer capable of identifying bombs from their remains or chemical signatures.
While details of their work remains secret, many of their conclusions become public when the investigators take to the witness stand as experts in prosecutions.
Once police have sealed a suspected bomb incident scene, the Forensic Explosive Laboratory's scientists, working with bomb disposal experts, assess the risks to the public and themselves posed by the device, particularly if it has not exploded.
Once scientists are sure that they can safely move a device or the remains, bomb disposal experts prepare it for the journey to the specialist laboratory.
Where a bomb has detonated, such as in the IRA's attacks on the capital, the critical issue is the search for remains of the bomb and clues towards the identity of those behind the device.
This can lead to literally thousands of boxes of rubble being taken to the laboratories. Once there, special machinery is used to first sort the rubble into different sizes before it is carefully dried out.
The scientists then essentially have two priorities - to establish the facts about the bomb and to uncover details critical for the police operation.
Different teams look for different things. Some scientists look for mechanical elements - such as remains of wires or timing devices.
Experts can spend weeks, if not months, sifting through box upon box of debris - usually with nothing more than a pair of tweezers.
Just one small piece of wire, tape or plastic may be a critical lead if police can link it to a suspect.
Others will look for the chemical "characteristics" of a device. These tell-tale chemical traces may again provide all-important evidence that allows the police to link a bombing to a suspect or a "bomb factory".
These procedures also help the scientists to build a chemical portrait of the bomb - meaning that it could be linked to previous explosions.
A third line of inquiry is to look for DNA or other evidence, such as clothes fibres, left on the device by the bomb-builder.