Updated

The U.S. put a price on the head of the ruthless leader of Nigeria’s Boko Haram long before he masterminded the kidnappings of hundreds of schoolgirls, but American forces are now poised to help hunt the shadowy warlord said to have a photographic memory.

Abubakar Shekau, who drew international ire and scorn after vowing to sell young Christian girls "in the marketplace," could soon be the subject of a multi-national manhunt involving U.S. military and law enforcement agents. But the hunt for the leader of the Islamic terror group Boko Haram, which loosely means “Western education is forbidden,” will be complicated by Shekau's well-documented resourcefulness - and low profile.

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Believed to be as young as 36 or as old as 45 — Shekau was Boko Haram’s second in command until founder Mohammed Yusuf was killed in a 2009 crackdown. Shekau was initially thought to have also been killed during those attacks, but he later surfaced in a video claiming to be the terror group’s new director.

The U.S. Department of State is offering a reward of up to $7 million for information leading to Shekau’s location. In 2012, he was declared as a “specially designated global terrorist” for numerous bombings, including the August 2011 attack on the UN office complex in Nigeria’s capital, Abuja, that killed 23 people and injured dozens more.

In February, Boko Haram gunmen stormed a secondary school in northeast Nigeria, locked a boys' dormitory and set it on fire, killing those who tried to flee and burning the rest alive. The humanitarian group Open Doors International said the attack killed more than 40 young boys.

Shekau, according to a BBC profile, is known as a “fearless loner” with a photographic memory, a complex and often paradoxical man who is part intellectual, part terrorist. His nickname — Darul Tawheed — translates as a specialist in Tawheed, or the concept of monotheism in Islam.

“He hardly talks,” one journalist, Ahmed Salkida, told BBC. “He is fearless … He is one of those who believes that you can sacrifice anything for your belief.”

Shekau does not speak English, but is fluent in his native Kanuri, Hausa and Arabic languages. He reportedly does not even communicate directly with the group’s soldiers.

“A lot of those calling themselves leaders in the group do not even have contact with him,” Salkida told BBC.

Shekau, according to those who study the group, is known for being particularly brutal.

“I enjoy killing anyone that God commands me to kill — the way I enjoy killing chickens and rams,” he said in a clip released in 2012 after an attack in Kano, Nigeria, that killed more than 180 people.

In addition to being the group’s militant leader, Shekau also serves as its spiritual leader, Salkida said.

“He has a photographic memory and is well versed in theology,” he told BBC.

Shekau recently took credit for the kidnapping of more than 300 girls in an hour-long video that opens with Boko Haram fighters firing guns into the air and shouting Allahu Akbar!"

"I abducted your girls," he said. "By Allah, I will sell them in the marketplace," he said in the video.

Kidnapped girls have reportedly been forced to marry their abductors — who paid a nominal bride price of $12 — or taken to neighboring Cameroon and Chad. An intermediary has told Nigeria's government that the terror group is willing to negotiate ransoms for the girls, and that two have died from snakebites and several more are ill. More than 280 remain in captivity and 53 have escaped, according to Nigerian police.