As the two men stepped out of their black cab and buzzed to be let into Graff Diamonds' exclusive New Bond Street store, the staff inside could have had no idea what was about to happen.
The men, however, had everything planned. Dressed in smart suits, they were aware they had to look the part to get inside. Once through the two doors and the security guard, they had planned which items they were there for. And, crucially, they knew exactly what they were going to do with their haul.
This last detail will trouble the most the Metropolitan Police's Flying Squad attempting to piece together a jigsaw of information they hope will tell them more about the men who managed to pull off Britain's biggest jewel heist in a busy London street in broad daylight.
A haul of £40m worth of diamond-encrusted jewellery and watches cannot be inconspicuously sold on. The thieves must have had a market for their goods in mind. It is also, according to those in the know, unlikely that the gang would attempt to sell the goods in Britain, due to the amount of publicity the case has already garnered.
Roy Ramm, a former Flying Squad Commander at Scotland Yard, explained: "The police will be asking themselves why these guys had the brass neck to go into a shop they knew would have CCTV, 'open faced' as it were.
"Obviously they wouldn't have got inside wearing masks but police will study the CCTV footage to see if any prosthetics or disguises were used. If not then they will ask why. The answer is probably that the men didn't care if they were caught on camera because they knew they were not going to be in the UK [afterwards]."
Yesterday the police announced that they had arrested a 50-year-old man in connection with the robbery at an address in Ilford, east London, on Monday and that he had been bailed the day after. Police sources say he is a "minor player" and was not involved in the robbery itself but detectives think he was involved in the planning. They have reiterated their desire to speak to the two men caught on CCTV.
But Mr Ramm said that the likelihood was that the men had already fled abroad, despite the fact that a warning was issued to all ports telling staff to be on the look-out. He said: "Selling stuff like this in Britain is very difficult because people know the items are stolen and I'd imagine Graff's insurers will put out a huge reward so the criminal fraternity here will be interested in that. Trying to sell here is too risky because the heat is on. It is probable that they have melted the jewellery down for the diamonds and taken them abroad." One valuer said this would reduce their value to £4m.
Mr Ramm added: "You then have to ask yourself where in the world people buy and wear huge gems. The answer is the middle east or the far east. That is the type of market they'll be looking at. Put it this way: these gems are not sitting under someone's pillow in Chigwell."
Thursday's raid is easily the biggest jewel heist in Britain. And it marks a trio of raids on Graff stores in London. The previous biggest was also at the New Bond Street store in 2003 when £23m worth of jewellery was stolen. That robbery was carried out by members of the Pink Panther Gang, an eastern European criminal cartel accused of some of the world's biggest robberies.
Members of that gang are believed to be responsible for another attack at Graff in Sloane Street in 2007, although no one has ever been caught for that raid. It is believed that police in the current investigation have not ruled out the possibility that the same gang has struck again, but think it is unlikely due to the fact that the suspected culprits in the latest raid had London accents.
The suspects in the latest raid arrived by black cab. Police initially appealed for the driver to come forward and the man has since done so. He is not being treated as a suspect but has been interviewed as a witness.
Inside the store they threatened staff with handguns, forcing one woman to open a glass cabinet from which they then stole 43 items, containing 1,500 gems, in just two minutes. They escaped by taking a member of staff hostage and then using four vehicles in an elaborate getaway during which they fired two gunshots to warn off members of the public. Police believe at least four men were involved in the robbery on the day and are studying CCTV footage from Graff and other shops and businesses in the street and along the escape route to identify other members of the gang.
Certainly at least one member of the gang will have been in the shop previously, conducting a reconnaissance mission. Yesterday mobile phone footage emerged which showed the moment that the two men escaped with their haul. The video was taken by a man on New Bond Street at the time the robbery happened. Officers have recovered two of the getaway vehicles, a blue BMW and a motorbike whose driver was seen to receive a package from the men in the BMW, and will be checking for forensic evidence and to see if the vehicles are registered to addresses.
Mr Ramm added: "The officers will have been looking for any DNA evidence the men might have left behind. They took a woman hostage so her clothing will have been examined as will any other member of staff's clothing that they touched.
"It is going to be a very tough case to solve because it has clearly been very well planned, but in saying that I am wary of giving the robbers too much praise. A heist might sound glamourous and sophisticated but these men are anything but."
Daylight robbery: The great diamond heists
*In May 2001 thieves stole £4m worth of Cartier jewellery from a warehouse at Southend airport. About 2,000 items were taken, mainly watches worth between £3,000 and £12,000 each. Despite a £75,000 reward it was not until May 2008 that arrests were made. Four men were arrested. Three will stand trial in October.
*In May 2003 members of the international criminal cartel dubbed the "Pink Panthers" staged a £23m heist at the New Bond Street branch of Graff jewellers. Two men, Nebojsa Denic, 34, and his boss, known as Marco, took three minutes to steal 47 items. Denic was sentenced in to 15 years in jail. A second man, Milan Jovetic, was also convicted, and sentenced to five and a half years. Marco was never found.
*In 2007 two men arrived in a chauffeured-driven Bentley at the Sloane Street branch of Graff, pretending to be wealthy diamond buyers before drawing silver handguns and demanding that staff hand £10m worth of jewellery. The store put up a £500,000 reward for information leading to a conviction but this failed to yield any arrests.
*In 2000 the "Great Dome" robbery, was foiled. The heist would have been the world's biggest diamond robbery, had it succeeded. A gang used a JCB digger to smash through the perimeter fence of the Millennium Dome to reach the De Beers diamonds, worth an estimated £350m. The gang members, from London and Kent, were aiming for the 203-carat Millennium Star – one of the world's most valuable cut stones – and 11 other "priceless" blue diamonds. But the jewels had been replaced with replicas by police and undercover officers pounced on the gang. Five men were sentenced on robbery charges.