SINGAPORE - Terrorists are constantly trying to outwit the authorities by coming up with weapons of destruction that can go undetected, evading sophisticated security systems.
1 SEPT 11, 2001
Members of the Al-Qaeda terrorist network steered two passenger jets into the twin towers of New York City's World Trade Centre.
A third aircraft hit the Pentagon in Washington and a fourth hijacked plane crashed in Pennsylvania. Nearly 3,000 people died in the attacks.
2 SHOE BOMB 2001
Richard Reid tried to blow up American Airlines Flight 63 from Paris to Miami on Dec 22, 2001, but failed when passengers overpowered him as he tried to light a fuse protruding from his shoe.
According to the Federal Bureau of Investigation, the sole of his shoe was packed with enough high explosives to blow up the fuselage of the aircraft. Reid pleaded guilty to terrorism charges and was jailed for life in the US.
3 UNDERWEAR BOMB 2009
The "underwear bomber", Nigerian Umar Farouk Abdulmutallab, was subdued by passengers and crew after trying to blow up an airliner heading to Detroit from Paris using explosives hidden in his undergarments.
He has been sentenced to life imprisonment. He smuggled more than 76g of explosives on board on Christmas Day in 2009.
The Al-Qaeda plot failed when the bomb did not detonate properly, instead causing a fire as the plane began its descent over Detroit.
4 PRINTER CARTRIDGE BOMB 2010
Yemen-based Al-Qaeda in the Arabian Peninsula has been linked to an attempt two years ago to blow up US-bound cargo planes with explosives concealed in printer cartridges.
The plot was uncovered following a tip-off from a former member of the Al-Qaeda, who said that UPS and FedEx packages carrying explosives had been mailed from the Yemeni capital of Sanaa to Chicago.
The UPS cargo plane stopped in Qatar, then Dubai, where local officials found the device inside a Hewlett-Packard printer. The FedEx cargo plane stopped at the East Midlands Airport in Britain, where the other bomb was found.
5 LIQUID BOMB 2013
Senior US officials have voiced growing concerns that a Yemen-based Al-Qaeda affiliate in the Arabian Peninsula may have developed a liquid explosive that could go undetected.
It is an explosive liquid in which ordinary clothing is dipped and becomes explosive when dry.
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