ISIS Leader Abu Bakr al-Baghdadi New Photo: Reveals Former Detainee at U.S. Prison in Iraq

An image of Abu Bakr al-Baghdadi obtained by CBS News and released on Feb. 17, 2015. | CBS NEWS

An image of a man who would later become the leader of the so-called Islamic State of Iraq and Syria was obtained by CBS News on Tuesday, in which he was shown being processed at a U.S. military prison in Iraq in 2004.

Abu Bakr al-Baghdadi, who worked as a university official at the time of his capture in the same year, was shown wearing a yellow prison jumpsuit that other prisoners were also wearing during their stay in Camp Bucca.

He has made only one public appearance so far since declaring himself a caliph and delivered a sermon at a mosque in Mosul in June last year.

Baghdadi encouraged his followers to "explode the volcanoes of jihad everywhere" in a purported audio recording of his speech which came out last November.

According to an investigation by CBS, Baghdadi was among at least a dozen ISIS top leaders who served time at Bucca, described as "one of the toughest American prisons in Iraq."

He spent 10 months in the prison, "a pressure cooker for extremism" according to U.S. officials who worked at Bucca from February to December 2004.

The same officials had expressed their concern over prisoners becoming radicalized. A rehabilitation program at the prison was established to counter extremism, but some who worked there said the program was not executed effectively.

The jihadists recently beheaded 21 Egyptian Coptic Christians who were taken from Libya earlier this year.

They also recently executed by burning around 45 people, many of whom were police officers, in the town of al-Baghdadi located in Iraq's Anbar province. The mass execution, the Examiner reported, coincided with President Barack Obama's launch of an international summit on the battle against "violent extremism" in Washington, D.C.

The town was captured by Islamic militants, a bold move considering that it is only five miles from an air base staffed by U.S. Marines, Fox News reported on Sunday. The terror group is reportedly moving to expand its current strongholds and to create militant affiliates in other countries.

Most of al-Baghdadi, which is 55 miles from the Anbar capital of Ramadi, were seized by ISIS fighters on Thursday. Iraqi soldiers fought back and retook some government buildings on Friday but withdrew the next day.

"Ninety percent of al-Baghdadi district has fallen under the control of the insurgents," a local Iraqi official was quoted as telling Reuters.

The town, attacked by militants from two directions before advancing inward, was the first territorial gain by the militant group in months.

A U.S. Central Command spokesman earlier denied reports on Sunday that ISIS had captured al-Baghdadi. "Al-Baghdadi has not fallen to ISIL or been seized by them," said the U.S. Central Command, in an email to Fox News.

Al-Baghdadi is "contested" not "Daesh held," continued the email. "Daesh" is the name used by Arab partners of the U.S. in referring to ISIS.