By Reevel Alderson
BBC Scotland's home affairs correspondent
From the moment police were called to investigate two suspected bombs in central London, the plotters were marked men.
Two mobile phones discovered in a Mercedes parked outside a nightclub gave them vital clues.
Each showed a number of missed calls.
These phones were to have been used to set off devastating bombs: the missed calls were the attempts to detonate the devices.
Each of the mobile phones showed a number of missed calls
But more crucially, the phones contained a wealth of material which meant police soon knew who they were hunting.
According to Deputy Assistant Commissioner John McDowall of the Metropolitan Police, Bilal Abdulla and Kafeel Ahmed would also have known that.
"We felt we were very, very close, and I think they themselves must have felt that closeness too, because they would have known what they had left behind in the vehicle. Obviously that was a huge help to us," he told BBC News.
In fact, police were at a taxi office in Paisley searching its records as the attack happened at Glasgow Airport.
Bilal Abdulla had regularly called the taxi firm to be driven between his home in Houston, Renfrewshire, and the Royal Alexandra Hospital in nearby Paisley where he worked.
Before the airport attack, police had also contacted a letting agency from where Abdulla had rented his house at 9 Neuk Crescent in Houston.
In the garage was a virtual bomb factory, with evidence of a further planned attack.
Even though Abdulla and Ahmed fled from London, using public transport along a circuitous route via Stratford, Stansted Airport and Stoke before heading to Scotland, police were still able to track them, thanks to signals from their phones.
Dr Ian Ferguson, of the Infomatics Group at Strathclyde University, explained that mobile phones were constantly in touch with local transmitters, giving the police a good idea of Abdulla and Ahmed's location.
"They can go to the mobile phone company and say: 'We have a phone number, can you tell us where it is, in relation to your system?' he said.
"They can then run the appropriate software on their system, and say 'this phone was last seen however long ago' - it can be minutes, seconds - 'and it was seen in proximity to that mast, that mast and that mast', and by triangulating, you can get a precision on where they are."
He explained that the mobile phone recovered from the blazing Jeep at Glasgow Airport, although badly damaged, yielded a goldmine of information - valuable as police built a case.
Tests carried out at Strathclyde University showed phones heated to 1,500C can still provide information, provided their chips are relatively intact.
Police can also track the movement of suspects using the system of automatic number plate recognition, provided by a network of traffic cars and roadside cameras.
Sgt Raymond Kerr, of Strathclyde Police, one of the officers who developed the system for use across Scotland, said it could be used live with commanders watching in control rooms.
"What it allows the police to do is to be more intelligence-led," he said.
"Where, in days gone past, you might have had long road checks at the side of the road, stopping numerous members of the motoring public, this now allows us to focus on people who are using vehicles in a criminal way."
Much of the information gained during the hunt for the plotters was augmented by more traditional forensic evidence such as CCTV footage.
It supplemented and corroborated the information obtained during the hunt for Abdulla and Kafeel Ahmed.
Ultimately, this helped prove the prosecution case which led to Abdulla's conviction.