A radical imam tied to the Fort Hood shooter and considered to be an Al Qaeda recruiter today could have been arrested on a felony warrant in 2002, but the U.S. Attorney in Denver rescinded the warrant for Anwar Awlaki, ABC News reported Monday. A day later, Awlaki was intercepted as a terrorist suspect at John F. Kennedy International Airport in New York but let go.

Awlaki, who was in frequent contact with Fort Hood killer Nidal Malik Hasan, is currently based in Yemen. A vocal supporter of terrorism, he praised Hasan as "a hero" for carrying out the Fort Hood attack.

Awlaki has been the inspiration for other terrorists. One of the men convicted of plotting an attack on Fort Dix, N.J. was videotaped expressing his admiration for Awlaki and recommending a lecture by the imam. Awlaki is also an inspirational leader to members of al-Shabaab, a Somali jihadist group. Read more about Awlaki here.

The decision to cancel the arrest warrant was made by David Gaouette, then an assistant U.S. Attorney responsible at the time for overseeing all terrorism cases in Colorado. In August, President Obama appointed Gaouette U.S. Attorney for Colorado.

The FBI investigated Awlaki in 1999 and 2000. It discovered that he had been in touch with an associate of Omar Abdel Rahman (the "Blind Sheik"), currently serving a life-plus-65-year sentence for his role in a conspiracy to attack New York landmarks. That Awlaki investigation was closed in 2000 due to lack of evidence.

But after September 11, Joint Terrorism Task Force agents in San Diego decided to take another look at Awlaki because of his connection to hijackers Nawaf Alhazmi and Khalid Almidhar. The two had attended a San Diego mosque headed by Awlaki. Authorities said the imam had had numerous closed-door meetings with the pair, leading investigators to believe he was their spiritual advisor and knew in advance about the September 11 attacks.

When Awlaki moved to Dar Al-Hijrah mosque in Falls Church, Virginia in early 2001, Alhazmi visited him there, along with a third September 11 hijacker, Hani Hanjour.

But investigators needed a reason to detain Awlaki and hold him in custody. They considered using the Mann Act, a federal law barring the interstate transport of women for "immoral purposes." Awlaki had been arrested twice for soliciting prostitutes in San Diego in the 1990s and had been seen crossing state lines with prostitutes in the D.C. area.

But before they could detain Awlaki, he left for Yemen in March 2002. Months later, investigators realized they could arrest him on passport fraud charges, a felony punishable by up to 10 years in prison. In October 2002, a federal judge signed an arrest warrant for Awlaki – who by that time was also on the U.S. government's terrorism watch list.

One former JTTF agent told ABC "We were ecstatic that we were able to get a warrant on this guy." But within days, Gaouette and the U.S. Attorney's Office in Denver quashed the warrant.

Awlaki arrived at JFK International Airport on October 10, 2002 – the morning after the warrant was cancelled. When he stepped off a Saudi Airlines flight from Riyadh, he was detained by U.S. Customs. But three hours later, after authorities learned the arrest warrant was no longer in effect, he was released and put on a flight to Washington, D.C. Authorities even thanked Awlaki and his family for their patience during the delay.

Awlaki subsequently went to Northern Virginia where he visited radical cleric Ali Al-Tamimi and reportedly inquired about recruiting Muslims for jihad. Tamimi is serving life plus 70 years in federal prison for inciting a group of young Muslim men to fight alongside the Taliban against the United States in Afghanistan after September 11. Awlaki left the United States sometime before the end of 2002, spending more than a year in Britain. In 2004, he moved to Yemen where he has become one of the leading voices preaching jihad against the West.