When the U.S. went to war with al Qaeda almost a decade ago after the terrorist organization launched a deadly attack against the U.S., killing thousands and taking down New York's World Trade Center towers, the contest seemed un-winnable at times. Over the past decade, some pundits and experts even labeled it that -- the un-winnable war. 

But now that the U.S. has reportedly killed al Qaeda's second-in-command in Pakistan, according to a senior Obama administration official, the reality that America will soon claim victory in the war against al Qaeda is becoming a reality.

Reportedly killed by the U.S. on Aug. 22 in Pakistan, Libyan national Atiyah Abd al-Rahman was the network's former leader who rose to al Qaeda's No. 2 spot after the U.S. killed al Qaeda leader Osama bin Laden in a raid on his compound in May.

The killing of al Qaeda's second-in-command is another major jolt to the terrorist group that orchestrated the Sept. 11, 2001 attacks on the U.S. For years after the U.S. attack which took down New York's World Trade Center towers and killed thousands, al Qaeda leaders were able to hide out and remain loosely organized.

But consistent pursuit by the U.S. has paid off, and now the terrorist organization is near complete defeat. Killing Osama bin Laden was the main objective, but taking out other leaders has been required to finish the task. Last month U.S. Defense Secretary Leon Panetta said al Qaeda was nearing defeat, but that the U.S. needed several more successful attacks to take out the last remaining key leaders.

Al-Rahman was killed Aug. 22 in the lawless Pakistani tribal region of Waziristan, according to the official said, who insisted on anonymity to discuss intelligence issues, according to The Associated Press.

The official would not say how al-Rahman was killed. But his death came on the same day that a CIA drone strike was reported in Waziristan. Such strikes by unmanned aircraft are Washington's weapon of choice for killing terrorists in the mountainous, hard-to-reach area along the Pakistan-Afghanistan border, the AP reported.

Believed to be in his mid-30s, al-Rahman was a close confidant of bin Laden. He once served as bin Laden's emissary to Iran. Al-Rahman was reportedly allowed to move freely in and out of Iran as part of that arrangement, officials said. They also have said al-Rahman has been operating out of Waziristan for some time.

Born in Libya, al-Rahman joined bin Laden as a teenager in Afghanistan to fight the Soviet Union.

After Navy SEALs killed bin Laden, they found evidence of al-Rahman's role as operational chief, U.S. officials have said.

Once considered an un-winnable war, the U.S. battle against al Qaeda's terrorist organized has been slow but effective. Panetta said last month taht terrorist groups can be defeated, even though America has fought al Qaeda for a decade.

Speaking with reporters aboard a U.S. Air Force jet on his way to Afghanistan in July, Panetta said the U.S. is within reach of defeating Al Qaeda, and all that remains is killing or capturing the terrorist group's remaining 10 to 20 leaders.

Earlier this summer, President Barack Obama announced recently the plan to withdraw 30,000 American troops from Afghanistan over the course of the next year and a half, but Panetta's remarks last month have been most definitive to date that the war against al Qaeda can be won.

If we can be successful at going after them, Panetta said aboard the U.S. Air Force jet in July, I think we can really undermine their ability to do any kind of planning to be able to conduct any kinds of attack on this country. That's why I think (Al Qaeda's defeat is) within reach.

Panetta put no timeline on America's victory over al Queda, saying only more work is required.

The U.S. landed a major victory in the spring when al Qaeda leader Osama bin Laden was killed. Al Qaeda issued a statement at the time saying the death of the group's leader, at the hands of U.S. armed forces on the hunt for him for a decade in response to the deadly attacks on America orchestrated on September 11, 2001, was a curse that chases the Americans and their agents and goes after them inside and outside their countries.

Al Qaeda further warned in the statement, issued in May, that bin Laden's death at the hands of U.S. forces would not be wasted in vain.

But Panetta, a former California congressman who once headed the CIA before he was chosen by Obama to replace Robert Gates as Defense Secretary, said in June the U.S., in the moment following bin Laden's death, was further turning up its pressure on al Qaeda to put maximum pressure on the organization because he believed that if we continue this effort we can really cripple Al Qaeda as a threat to this country.

Among the 10 to 20 al Qaeda leaders remaining at large the U.S. needs to kill or capture is Ayman al Zawahiri, an Egyptian who succeeded bin Laden at al Qaeda's top leader when bin Laden was killed. the U.S. thinks Ayman al Zawahiri is hiding in Pakistan's Federally Administered Tribal Areas, a remote region along the Afghanistan border. The U.S. has sought Pakistan's help in finding Zawahiri.

Zawahiri is one of those (terrorist leaders at large) we would like to see the Pakistani's target along with our help, Panetta said.

While some al Qaeda leaders remain at large, the death of bin Laden followed by the death of the organization's number two leader means that America is close, finally, to claiming victory in the so-called un-winnable war.