The top terror leader later regularly visited the compound to meet with Sayyaf and to repeatedly sexually assault Mueller, officials said.
In early February ISIS claimed Mueller had been killed in a coalition bombardment in Syria. Three months later, on May 16, the U.S. Army's elite hostage-rescue and counter-terrorism unit known as Delta Force conducted a ground raid to capture Abu Sayyaf but was forced to kill him instead when he raised a weapon, officials said.
The new revelations about Mueller's long ordeal -- which involved torture since the beginning of her one-and-a-half years of captivity, her family has been told by the FBI -- shatter rumors spread by some officials that she had cooperated or was a willing spouse, which has deeply upset her family and many inside her case.
Some speculation was based on a smuggled letter released by her family in which the captive Mueller wrote, about a year into her captivity, that she was "completely unharmed + healthy (put on weight in fact); I have been treated w/ the utmost respect + kindness."