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ISIS militant who held Kayla Mueller captive is not being charged in U.S.

The Islamic State militant who held American hostage Kayla Mueller captive is not being charged in the U.S. for her crimes.

Nasrin As'ad Ibrahim, also known as Umm Sayyaf, had been held by American military interrogators since May, after U.S. Special Forces captured her during a raid in Syria. Late Thursday, the U.S. transferred her into the custody of the Iraqi Kurdish courts.

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White House Spokesman Josh Earnest said that the Justice Department, along with other U.S. agencies, came to a "unanimous decision" to hand Umm Sayyaf over to Iraq, despite their confidence that she played an important role within ISIS and was "complicit" in Kayla Mueller's captivity.

Earnest cited diplomatic and legal factors as some of the considerations behind the decision not to bring Umm Sayyaf to be tried in a U.S. court.

American officials confirmed that they had explored charging Umm Sayyaf and bringing her to the U.S. but ultimately decided not to indict her at this time.

A Justice Department spokesperson told CBS News that while he "cannot speculate about potential charges" against Umm Sayyaf, he emphasized that "the U.S. justice system remains a powerful tool to bring to bear against those who harm our citizens abroad."

One factor in the decision was Umm Sayyaf's Iraqi citizenship, a State Department official explained. The Iraqi constitution explicitly bans the transfer of any Iraqi to a foreign government. However, the U.S. did succeed in getting Baghdad to sign off on the transfer to Kurdish authorities. The Iraqi legal system allows for the death penalty.

Earnest said the Obama Administration is confident that Umm Sayyaf will be brought to justice. U.S. interrogators have spent many months extracting information from her. And U.S. intelligence has indicated she has given them useable information regarding the inner workings of ISIS' finances. Umm Sayyaf's husband - often referred to as the chief financial officer of ISIS - was killed by U.S. Special Forces during a May raid.

There has not been any official public disclosure by the U.S. about the circumstances surrounding the death of 26 year old American aid worker Kayla Mueller. She was the only female among the four American hostages captured and killed by ISIS in Syria.

ISIS claimed that she was killed when a Jordanian airstrike hit the extremists' stronghold of Raqqa, which U.S. and Jordanian officials deny.

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