Cargo plane bomb found in Britain was primed to blow up over US

Device thought to have been sent by Yemen-based al-Qaida made safe three hours from explosion
A forensic officer removes a package from a UPS container at East Midlands Airport
A forensic officer removes a package from a UPS container at East Midlands Airport in Castle Donington. Photograph: Darren Staples/Reuters

The shocking reality of the terrorist printer cartridge bomb plot emerged today when Scotland Yard revealed that the device taken from a plane in Britain was timed to explode in mid-air over the eastern United States.

The bomb was found by police on board a cargo plane at East Midlands airport last month after detailed information was passed through intelligence channels to the UK and US from Saudi Arabia.

The Guardian understands that an alarm clock on a mobile phone attached to the printer bomb was set to go off at 10.30am BST. Tests revealed that if the cargo plane's journey had gone to schedule, the device – in a package addressed to a synagogue in Chicago – would have gone off in midair over the eastern seaboard of the US.

The device found in the UK was one of two discovered after a Saudi tip-off. The other was at Dubai airport. Both were capable of bringing down an aircraft.

The bombs are believed by western intelligence to have been sent by the Yemen-based al-Qaida in the Arabian Peninsula (AQAP), and sparked fears that a new vulnerability in aviation security has been discovered by the terrorists.

Both bombs contained at least 300 grammes of the explosive pentaerythritol tetranitrate, or PETN. The device found in Dubai had travelled on two passenger planes without being detected.

The bomb found aboard a UPS plane at East Midlands was so sophisticated that it was initially cleared by military and police explosives experts. When the plane landed at 2.13am after arriving from Cologne, police were waiting for it. Saudi intelligence told them which package to look for and it was taken off the plane.

At 4.20am the plane was allowed to continue on its journey as examination of a large device containing a printer cartridge continued. It emerged yesterday that the bomb was made safe inadvertently by bomb experts. At 7.40am they had not determined that the package was a bomb and stopped it from exploding by removing the "printer cartridge from the printer", police said. The bomb was due to explode just three hours later.

By mid-morning safety cordons at East Midlands were taken down, but when UK authorities were alerted about the Dubai bomb, experts re-examined the East Midlands device. A senior counter terrorism official told the Guardian the device was "one of the most sophisticated we've seen. The naked eye won't pick it up, experienced bomb officers did not see it, x-ray screening is highly unlikely to catch it."

According to well-placed sources, investigators believe the plotters intended both bombs to detonate over America. That was the assumption from the moment intelligence agencies in the US and the UK were tipped off by the Saudis. That view was strengthened by the early discovery that both the bomb on the UPS plane and the one found on a Fedex plane in Dubai earlier were wired to circuit boards from mobile phones that did not contain Sim cards, which are needed to receive calls. This points to phones being used as timers.

However, some counter-terrorist sources question that certainty. Given the vagaries of cargo timetables they say it was impossible for the plotters to know where the bombs would have detonated.

This explains remarks made by Theresa May, the home secretary, on 30 October, the day after the bombs were found. She said, after a meeting of Cobra, the government's emergency planning committee: "We do not believe the perpetrators would have known the location of the device when it was planned to explode."

Officials have been trying to establish what the terrorist targets were. When the bombs were set to go off is central to the investigation because it could indicate whether the terrorists wanted to blow up the planes in US airspace or take them down regardless of location.

In a statement Scotland Yard said: "Forensic examination has indicated that if the device had activated it would have been at 10.30am BST on Friday, 29 October 2010. If the device had not been removed from the aircraft the activation could have occurred over the eastern seaboard of the US. The device was disrupted at East Midlands airport by explosive officers during the initial examination when they removed the printer cartridge from the printer at approximately 7.40am on Friday 29 October 2010."

In the US the news was seen as further evidence that AQAP had moved to the top of the country's security concerns.

With confirmation that the plot was aimed at bringing down planes over American territory, that stance appears to have been justified, officials said. White House spokesman Nick Shapiro told CNN the findings by British police "underscore the serious nature of the attempted AQAP attack and the challenge we all face in trying to prevent or disrupt such attacks."

But, Shapiro added, the fact that the plot had been detected was testimony to the success of international intelligence agencies working together.

Continued co-operation over the situation in Yemen was needed, he added. "The United States will continue to work closely with these partners and the government of Yemen to address and counter the threat posed by AQAP as well as to provide humanitarian and economic assistance to help shape a stable and secure Yemen."

Attacks on US

Since 11 September 2001, there have been several attempts to attack US interests.

22 December 2001

British citizen Richard Reid tried to ignite a shoe bomb on an American Airlines flight to Miami.

6 March 2009

Kevin James was jailed for 16 years for planning to attack US military operations.

12 August 2009

Ehsanul Islam Sadequee found guilty of aiding terror groups by sending videos of US landmarks overseas.

25 December 2009

Umar Farouk Abdulmutallab tried to blow up a Delta airlines plane to Detroit with a bomb hidden in his underpants.

1 May 2010

Faisal Shahzad made a failed attempt to blow up a 4x4 parked in Times Square, New York.