Massive investigation operation follows London attack
Forensics and intelligence evidence will underpin efforts to find those responsible for London's worst ever terrorist attack.
Bombs exploded during the morning rush hour on three London Underground trains and one double-decker on 7 July, killing at least 50 people and leaving hundreds more injured.
Police have begun painstakingly analysing evidence and the UK's intelligence agencies have begun searching for clues that could help trace those responsible for the attacks.
Forensic officers will search the scene of each blast for valuable evidence including traces of explosive and DNA samples. Identifying the explosives used could help investigators link the attacks to other terrorist acts and DNA could perhaps be linked to known terror suspects. Scene-of-crime investigators typically recover and preserve every piece of material before reconstructing the scene in an aircraft hanger for further analysis.
Murder squad detectives, drafted in to assist Anti-Terrorist Squad officers analyse evidence, will help examine hours of CCTV footage in an effort to spot passengers carrying bags on to trains before leaving a station without their luggage. And police will also try to gather information from eye witnesses involved in each event.
But the forensic inquiry is likely to be complicated and time consuming. There are several different scenes to investigate and at least one of these scenes - the tunnel between Kings Cross and Russell Square - may be structurally unsound.
"There are people who monitor phone calls and emails for a living and they will be going back through their records using automated tools," Pike told New Scientist. He adds more traditional intelligence sources, such as operatives working in the UK and abroad, would also be tapped for new facts.
An important clue could be the similarity between this attack and the bombings carried out by Al-Qaida in Madrid, 2004, in which 191 people were killed. In the Spanish attacks, morning rush hour trains were also targeted in a coordinated manner, but it is not yet clear whether similar explosives and trigger devices were used in this latest attack.
Spanish security services have previously warned Scotland Yard that the North African wing of Al-Qaida blamed for the Madrid attacks could have links in London. And Mustafa Setmariam Nasar, who is thought to have masterminded the Madrid bombings, lived in London during the 1990s, when he might have established so-called "sleeper cells" primed to carry out future terror strikes.
Shortly after the London travel network was struck, a previously unknown Islamic group, calling itself the Group of al-Qaeda of Jihad Organisation in Europe, posted a statement to a website claiming responsibility.