US-born Islamic cleric Anwar al-Awlaqi, killed in a US drone attack in Yemen last year, had been in US custody at least twice in prior years but was released, a human rights group said.
Judicial Watch, an accountability watchdog group, said it had learned this through Freedom of Information lawsuits it filed with the US government.
It said documents from the US embassy in Yemen, for instance, indicate Awlaqi was held for at least eight months between late 2006 and mid 2007. But the documents do not say how long he was held or why he was he was freed.
Back in October 2002, Awlaqi was detained at New York City's John F. Kennedy International Airport on a warrant for passport fraud, a felony that can be punished with up to 10 years in jail.
But the FBI ordered his release, Judicial Watch said. Awlaqi flew to Washington, DC and eventually returned to Yemen.
In yet another incident, months before Awlaqi was killed in September 2011, the embassy in Yemen was instructed to send Awlaqi a letter urging him to come to the embassy to pick up an important document but not tell him what it was.
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In fact, it was simply a revocation of his passport, Judicial Watch said.
"These documents provide further evidence that the federal government, under both the (George W.) Bush and Obama administrations, has been operating a 'catch and release' program for terrorists," said Judicial Watch President Tom Fitton.
"The idea of inviting al-Awlaqi, a known terrorist, to our embassy in Yemen in order to revoke his passport is beyond belief," Fitton said.
Prior to his killing Awlaqi had been described by the United States as head of external operations for Al-Qaeda in the Arabian Peninsula -- a Yemen-based group currently believed to be the terror network's most effective and lethal franchise.
Awlaqi, a charismatic preacher who was fluent in Arabic and English, was considered a particularly effective global recruiter.
President Barack Obama in 2010 had authorized the man's targeted killing after intelligence agencies concluded he was involved in anti-US plots. This targeting was unprecedented _ and polemic _ for an American citizen.
US officials believe Awlaqi played a significant role in the attempt to bring down a US airliner over Detroit by an assailant with explosives sewn into his underwear on December 25, 2009.
He was also believed to have coordinated the thwarted 2010 plot to blow up cargo aircraft bound for the United States and had called for attacks against US and Arab governments.