Timeline: A Look Back at Attacks on the Pentagon

A Marine Corps reservist who was later identified as Yonathan Melaku, 22 of Alexandria, Va., was arrested early Friday morning on suspicion of carrying materials to make a bomb. Along with several Ziploc type bags containing suspicious substances, ABC News reports Melaku was carrying a notebook that had several pro-al Qaeda statements scribbled in it and a page containing the phrases "al Qaeda," "Taliban rules," "mujahidin," and "defeated coalition forces."

Brenda Heck, special agent in charge of counter-terrorism for the FBI, later said, "There was not a device and the products found are determined right now to be inert." The Pentagon as well as several surrounding areas were closed to traffic, causing the morning rush hour to crawl to a halt.

Let's take a look back at other threats and attacks carried out on the Pentagon over the years.

May 19, 1972

A group called the Weather Underground claimed responsibility for a bomb that exploded in the women's restroom on the fourth floor of the Pentagon. The bombing which caused no reported injuries, was said to commemorate Ho Chi Minh's birthday, according to CBS Evening News. There were few on duty during the blast, but several Air Force computers were damaged by water from broken pipes. The damages were estimated at $80,000, and several new security measures were scheduled to be implemented within hours after the explosion due to anti-war demonstrations.

Sept. 11, 2001

On the morning of September 11, 2001, American Airlines Flight 77 was hijacked by suspected terrorists and expertly flown into the western side of the Pentagon, killing a total of 189 people. The five hijackers on the plane perished along with 59 passengers and 125 Pentagon employees. The Pentagon attack was just a small part of a much larger terrorist conspiracy that saw three other planes hijacked, two of which were successfully flown into the Twin Towers in New York's financial district. The government speculates a fourth plane was headed to the White House when the passengers intervened.

One bright spot in the Pentagon attacks was that the area where the plane crashed was under renovation, and was only occupied by 800 of the usual 4,500 employees who would normally be present. In addition to the substantially smaller population, the area hit was best prepared for such an attack due to its proximity to the Heliport Entrance, and was the only area of the Pentagon with a sprinkler system. The terrorist attack was the worst coordinated attack on American soil in history and gave new meaning to the number 911 in the American lexicon.

March 4, 2010

Around 6:40 p.m. John Patrick Bedell, 36, calmly walked up to an entrance and opened fire on two police officers, reports the Washington Post. The officers were not seriously injured, and returned fire, critically wounding the assailant. Bedell was a computer programmer from Hollister, Calif., who had been institutionalized several times for bipolar disorder. Bedell had been openly critical of the government, and was a follower of the 9/11 truth movement. He believed the Sept. 11 attacks were faked, and envisioned a monetary system where marijuana took the form of currency. He kept a blog on blogspot titled rothbardix that he used to blast the government and foreshadow his actions on March 4. The truth about why Bedell committed the attacks will never be known: He died March 5 of a gunshot wound to the head.

Oct. 19, 2010

Shortly before 5 a.m., one or more unidentified assailants fired 10 shots at the south side of the Pentagon. CNN reports five shots hit glass windows, and five others hit metal panels. No one was injured, as the portion of the building targeted was being renovated, and the glass is bulletproof. Authorities shut down the entire Pentagon for 40 minutes and conducted a sweep of the entire building. Steven E. Calvary, director of the Pentagon Force Protection agency, called the incident "An isolated event." No one was ever charged or took credit for the attacks. The FBI later confirmed that the suspect who fired a high powered rifle at the Pentagon was the same person who fired on the Marine Corps. Museum and Marine Recruiting Center the same night, according to the Associated Press.