On October 29, 2010, two packages, each containing a bomb consisting of 300 to 400 grams (11–14 oz) of plastic explosives and a detonating mechanism, were found on separate cargo planes. The bombs were discovered as a result of intelligence received from Saudi Arabia's security chief. They were bound from Yemen to the United States, and were discovered at en route stop-overs, one at East Midlands Airport in the UK and one in Dubai in the United Arab Emirates.
One week later, al-Qaeda in the Arabian Peninsula (AQAP) took responsibility for the plot, and for the crash of UPS Airlines Flight 6. U.S. and British authorities believed Anwar al-Awlaki of AQAP was behind the bombing attempts, and that the bombs were most likely constructed by AQAP's main explosives expert, Ibrahim Hassan al-Asiri. The bombs were probably designed to detonate mid-air, with the intention of destroying both planes over Chicago or another city in the U.S. Each bomb had already been transported on passenger and cargo planes at the time of discovery.
...The UPS plane landed at East Midlands Airport at 2:13 AM local time on October 29. British military and police explosives experts had been alerted to the existence of the bomb, and conducted an initial search of the plane's cargo in the airport's UPS parcels distribution depot. Officers from the Scotland Yard Counter Terrorism Command joined them.
U.S. authorities provided the precise tracking number of the package, and the printer was scanned with explosives detection equipment, x-rayed, subjected to chemical swabs, and sniffed by sniffer dogs. No explosives were detected. Removing the suspect package for further examination, the authorities allowed the UPS plane to proceed to Philadelphia at 4:20 AM local time. At 10 am the British gave the all-clear, and removed safety cordons from the airport.
Later forensic examination indicated that the bomb was inadvertently disarmed by Scotland Yard explosive officers, who took the printer cartridge out of the printer during their examination that morning, around three hours before the bomb was due to explode at 10:30 AM (5:30 AM Eastern time). The officers were unaware when they took the device apart that it was a bomb. [
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British officials continued to believe that there were not any explosives in the package, but U.S. authorities insisted that the package be inspected again. British authorities then consulted with officials in Dubai, who had discovered a similar bomb in a computer printer cartridge, and MI6 spoke with the Saudi tipster. Scotland Yard explosives officers flew the printer and the cartridge in a police helicopter to the Defence Science and Technology Laboratory at Fort Halstead near London, and discovered the bomb at around 2 PM.