A man sets on fire a representation of a US flag, in an annual state-backed rally in front of the former US Embassy in Tehran, Iran, on Nov. 4, marking the anniversary of the seizure of the US Embassy by militant students on Nov. 4, 1979. On that day, militant Iranian students who believed the embassy was a center of plots against the Persian country held 52 Americans hostage for 444 days. The US severed diplomatic ties in response, and the two countries have not had formal relations since. Vahid Salemi/AP
Wrecked houses and a deep gash in the ground are shown in the village of Lockerbie, Scotland – damage caused by the crash of Pan Am Flight 103 on Dec. 21, 1988. Late libyan leader Muammar Qaddafi’s death on Oct. 20 resonates with the families who had loved ones on the airliner and who held Qaddafi responsible for sanctioning the bombing that killed 270 people. Martin Cleaver/AP/File
Fire, police, and other emergency vehicles block the street near the twin towers of New York's World Trade Center on Feb. 26, 1993, after an explosion in the underground parking garage killed six people and injured about 1,000. George Widman/AP/File
A bulldozer demolishes the bombed out building of the American embassy in Beirut, Lebanon, in this undated photo. The embassy was destroyed in a suicide attack by a pro-Iranian militant that killed 17 Americans on April 18, 1983. Reuters/File
The north side of the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma, is shown after a truck bomb explosion on April 19, 1995. One hundred and sixty-eight people were killed, including 19 children and one person who died in a rescue effort. Timothy McVeigh and Terry Nichols were convicted in the antigovernment plot to avenge the Branch Davidian standoff in Waco, Tex., exactly two years earlier.
US and Saudi military personnel survey the damage to Khobar Towers the day after the explosion of a fuel truck on June 25, 1996, outside the northern fence of the facility on King Abdul Aziz Air Base near Dhahran, Saudi Arabia. Alleged members of Islamic militant group Hezbollah were indicted on charges relating to the attack in June 2001.
Onlookers stand at the foot of damaged buildings in Nairobi, Kenya, after a huge explosion destroyed the US Embassy on Aug. 7, 1998, killing 213. Four men connected with Al Qaeda were convicted of the killings in May 2001 and later sentenced to life in prison. Sayyid Azim/AP/File
A United States Marine talks with an FBI investigator in front of the damaged US Embassy in the capital Dar es Salaam, Tanzania, on Aug. 15, 1998. The embassy was bombed on Aug. 7, 1998, killing 11 people. Osama bin Laden was blamed for the 1998 embassy bombings in Kenya and Tanzania. Brennan Linsley/AP/File
The port side damage to the United States Navy destroyer USS Cole is pictured after a bomb attack during a refueling operation in the port of Aden, Yemen, on October 12, 2000. Seventeen sailors were killed. The attack was linked to Osama bin Laden and other members of the Al Qaeda terrorist network.
Aladin Abdel Naby/Reuters/File
In the most devastating terrorist onslaughts ever waged against the United States, knife-wielding hijackers crashed two airliners into the World Trade Center on Sept. 11, 2001, toppling its twin 110-story towers. Al Qaeda was blamed for the attack that killed 2,749 people in New York. Carmen Taylor/AP/File
A helicopter flies over the Pentagon in Washington on Sept. 11, 2001, as smoke billows over the building. The Pentagon took a direct, devastating hit from an aircraft, and 184 people were killed in an attack blamed on Al Qaeda. Heenson Yim/AP/File
The Flight 93 National Memorial was dedicated in Shanksville, Penn., ten years after the hijacked United Airlines plane crashed on Sept. 11, 2001, during terrorist attacks that were blamed on Al Qaeda. Construction on the memorial began in 2009, but the effort still needs to raise $10 million to build a visitors center and memorial groves to the 40 passengers and crew who died. Curtis Tate/MCT/File
The aftermath of a bombing on May 12, 2003, in the Saudi Arabian capital of Riyadh is seen in this image made from television on May 13, 2003. Hours before a visit by US Secretary of State Colin Powell, attackers shot their way into three gated compounds housing Westerners, killing at least three and injuring about 60. Saudi TV via APTN/AP/File
A video grab image shows smoke rising from the US Consulate in the Saudi Arabian city of Jeddah on Dec. 6, 2004. Saudi security forces killed one of the gunmen and arrested two others, security sources said. Attackers had stormed the US mission, killing five consulate employees. Al-Ekhbaria/Via ReutersTV/Reuters/File
A Jordanian policeman stands guard under the wrecked, bomb-damaged wedding hall at the Radisson hotel in Amman, Jordan, on Nov. 10, 2005. Al Qaeda issued an Internet claim of responsibility for three suicide bomb attacks on Western hotels on Nov. 9, 2005, that killed 57 people, linking the deadly blasts to the war in Iraq and calling Amman the 'backyard garden' for US operations. Hussein Malla/AP/File
Rescue personnel work to clear the rubble from the site of a United Nations building in Algiers, Algeria, on Dec. 12, 2007, after twin truck bombings by an affiliate of Al Qaeda killed at least 31 people, on Dec. 11, 2007. AP
Smoke billows outside the US embassy in Sanaa, Yemen, on Sept. 17, 2008. A car bomb set off a series of explosions outside the heavily fortified embassy and killed 16 people on Sept. 16, 2008. Al Qaeda was suspected. Yemen News Agency/Reuters/File
The roadside bombs (improvised explosive devices) so deadly to US troops in Afghanistan are also being deployed against Americans at home, as the Pentagon adapts wartime strategies to help counter the threat.
ByAnna Mulrine, Staff writer
Timothy A. Clary/AFP/File
What is the danger that improvised explosive devices – the sorts of roadside bombs routinely used in Afghanistan, for example – could be used on highway overpasses in the United States?