(CNN) -- Born and educated in the United States, how did Anwar al-Awlaki, a charismatic Muslim cleric, go from "all-American boy" to a terrorist spokesman and recruiter for al Qaeda in the Arabian Peninsula?
His killing, announced Friday, is seen as a hit against al Qaeda's recruiting and fund-raising.
The transformation from an imam who originally condemned the 9/11 attacks to a key al Qaeda operative took place over a number of years, as the war on terror expanded and as he found himself caught up in it.
Al-Awlaki was regarded by the United States as one of the biggest threats to homeland security. Under his guidance, AQAP attempted to blow up a plane over Detroit on Christmas Day 2009 and in October 2010 dispatched two printer bomb packages from Yemen's capital, Sanaa, that were timed to explode over the Eastern seaboard of the United States, U.S. officials have said.
He was also believed to have influenced Fort Hood shooter Maj. Nidal Hasan, who authorities say killed a dozen soldiers and a civilian in a rampage at the Texas base.
Al-Awlaki was killed in Yemen when an airstrike hit his motorcade, a Yemeni official said Friday.
He was born in Las Cruces, New Mexico on April 21, 1971, and lived in the United States until age 7, when his family returned to Yemen. He returned to the United States in 1991 to complete a civil engineering degree at Colorado State University in Fort Collins, Colorado and later a masters in education from San Diego State University in California. He also attended a doctoral human resources program at George Washington University in Washington. In all, he was in the United States until 2002.
Authorities note that he was arrested in San Diego in 1996 and 1997 for soliciting prostitutes.
He was an imam in California and Virginia, where he preached to and interacted with three of the 9/11 hijackers, according to the 9/11 Commission Report.
He condemned the attack, but according to his father, the expansion of the war on terror became a turning point for al-Awlaki, especially after he got caught up in it.
Al-Awlaki spent 18 months in prison in Yemen in 2006 and 2007 on kidnapping charges, but was released without going to trial.
"They put him in jail for 18 months, and I detected a change after he got out of prison; he began to get away from the mainstream," his father, Nasser al-Awlaki told CNN last year.
A U.S. security official said last year that al-Awlaki's transformation from inspirational leader to operational recruiter for al Qaeda was first picked up in the early part of 2009.
By 2010, the U.S. Treasury Department named him a specially designated global terrorist.
In November of that year, al-Awlaki was charged in absentia in Yemen with incitement to kill foreigners. These charges stemmed from his alleged involvement in the Christmas Day 2009 plot and the Fort Hood shooting.
In January of this year, he was sentenced by a Yemeni court to 10 years in prison. But he remained in hiding.
Al-Awlaki and AQAP used the political turmoil in Yemen to expand its safe haven in the southern part of the country.
The elder al-Awlaki is an accomplished academic and had held several positions within the Yemeni government, including minister of agriculture. In the face of mounting intelligence, he denied that his son was a member of al Qaeda.
"I am now afraid of what they will do with my son, he's not Osama Bin Laden, they want to make something out of him that he's not," Nasser al-Awlaki said.
"He lived his life in America, he's an all-American boy," he added in last year's interview.
The father also warned that the aggressive hunt for his son and al Qaeda operatives in Yemen using missile strikes only serve to recruit more members to the organization.
Given these challenges of finding high-level targets, the Obama administration adopted a policy of pursuing terrorists unilaterally in other countries in some instances.
"The United States does not view our authority to use military force against al Qaeda as being restricted solely to 'hot' battlefields like Afghanistan, we reserve the right to take unilateral action if or when other governments are unwilling or unable to take the necessary actions themselves," White House counterterrorism adviser John Brennan said at a recent speech at Harvard Law School.
It was not immediately known what role the United States played in the killing of al-Awlaki.
But U.S. officials had announced that they would target him if they located him.
In May of this year, al-Awlaki survived an American drone assault after he switched vehicles.
Nasser al-Awlaki had gone to court in the United States in an attempt to have an injunction issued to prevent the government from targeting his son, but a judge threw out the case, ruling that he did not have standing to sue.
CNN's Paula Hancocks, Adam Levine and Jennifer Rizzo contributed to this report.