Before Islamic militants brutally executed an American journalist last week, they issued a series of demands. Alongside a ransom—more than $130 million—the Islamic State in Iraq and Syria wanted a number of prisoners freed from U.S. custody. One of them was Aafia Siddiqui, whose name came up again in a list of demands ISIS released Tuesday in connection to a second American hostage in its custody.

That second captive is a 26-year-old American woman who was kidnapped while doing humanitarian aid work in Syria last year. In return for her freedom, ISIS is demanding a $6.6 million ransom, along with Siddiqui's release.

Just who is Aafia Siddiqui, the Pakistani woman whose freedom makes the list of demands from one of the most extreme militant groups in the world?

Siddiqui has been called many things: "Most wanted" by the U.S. government in 2004 and "Al-Qaida Mom" by The New York Post soon thereafter, "the most important catch in five years" by a CIA operative after she was apprehended, and a "widely respected" Muslim and humanitarian by the Peace Through Justice Foundation, an advocacy group campaigning for Siddiqui's release.

Born in Karachi, Pakistan, to a middle-class family, Siddiqui, now 42, was educated in the U.S. She has a degree in biology from the Massachusetts Institute of Technology and received a doctorate in cognitive neuroscience from Brandeis. She moved to Boston, married a young doctor from her hometown, and was active at her mosque, raising money for humanitarian causes and handing out English-language copies of the Koran to non-Muslims. Shortly after 9/11, she and her husband were questioned by the FBI about a suspicious online purchase of body armor and $10,000 worth of night-vision equipment, which her husband explained away as intended for "big-game hunting in Pakistan." A few months later, the couple moved back to Pakistan, and soon divorced.

The rest of the story is murky. Siddiqui returned to the U.S. in 2002, allegedly for job interviews in the Baltimore area. There, she opened a P.O. box under the name of Majid Khan, who was later accused of planning to blow up gas stations in the area. When she returned to Pakistan, she married Ammar al-Baluchi, nephew of Khalid Sheikh Mohammed, the man who masterminded the 9/11 attacks. When Mohammed was caught and interrogated by the CIA the following year, it is believed that he pointed fingers at Siddiqui for her involvement in al-Qaida. She went underground.

What she did for the next five years is unclear. According to the U.S., she was in hiding in Pakistan, working for al-Qaida. She and her supporters claim that she was arrested and spent the years at an American detention facility in Bagram, outside of Kabul, Afghanistan. Either way, she turned up in July 2008, when she was arrested by Afghan police who thought she was going to blow up a mosque in Ghazni. They found incriminating evidence in her bag—chemicals and blueprints to U.S. targets such as the Statue of Liberty and the Brooklyn Bridge—evidence her lawyer says was planted on her by her former captors. The police turned her over to American forces.

During an interrogation, the FBI says that Siddiqui grabbed a U.S. officer's gun and fired at him, exclaiming "her intent and desire to kill Americans." She was shot in the resulting struggle, patched up by American medics, and later flown to New York. In 2010, a federal court sentenced her to 86 years in prison for the attempted murder of U.S. nationals. She is being held at a federal prison in Fort Worth, Texas.

Since her capture, Siddiqui has found supporters who range from ordinary Pakistanis unhappy with their government's cooperation with the U.S. to the Taliban and al-Qaida, who have also named her in lists of demands for prisoner swaps. Siddiqui was considered for the swap that won the freedom of U.S. Sgt. Bowe Bergdahl, Foreign Policy reports.

ISIS is the most recent terrorist organization to call for her release, and Siddiqui's relatives, who want her freed from prison, have not welcomed its involvement. In a letter to the family of the female American aid worker being ransomed by ISIS, Siddiqui's family members wrote, "associating Aafia's name with acts of violence is against everything we are struggling for."

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